I have two 85 300d's one is a grey market and newest one is American. I bought this car from an online dealer auction cheap. It has 145,000 miles and perfect leather interior and excellent paint. All systems work such as the cruise control, tach, all gauges, heat and air. In most respects it is much better than my grey market. The main problem as in most 300d's is the trunk. Both wheel wells are rotten. The rust is only in the wells not on the outside body panels. I am considering keeping this car and selling the grey market. What I am wondering is, How much can I expect to pay for the wheel well repair? Both sides need replacing. By the way I see no other rust on the car except for 2 two or three small rock chips. Thanks in advance for all your advice.

I would clean the wheel wells up as best as you can and coat then with POR15. It only requires that you remove the loose scale. Are you sure there was not an earlier repair? These are prone to this problem.
Ron

I sure it has not been repaired before, I might be able to use the POR15 on the driver side but the passanger side is really bad, I can push my finger through some of it.

This is a unibody car and wheel wells may be structual. If car has had a repaint at some point check the outer wheel well flange with a magnet. If the outer flange is okay start to probe inner wheel wells as some just have rust an inch or two in past the outer lip. For those an aftermarket patch panel is available punched out to about five inches depth that can result in a good economical repair. These patch panels are made in denmark and available through most UAP etc type places.(20-30.00 per side) If the whole wheel well is rotten that is a different story. Again if you can see that the car has had a repaint at some stage get it up on a hoist and start looking around the jack points, general rocker panels, floors etc very careully. In fact probe with screwdriver or pick. I have one 240d with this rust pattern in storage waiting to get to it. Rear inner fenders are rotten for about the first two or three inches in. Seem solid past that. Outer fenders are rotted for about 2 inches up as well. Floor, trunk and rest of wells are just about perfect so will weld inner and outer patches in and paint. Rust patterns seem to vary all over the country and even find different patterns in same areas sometimes. Just strange. Just like yours I picked up very cheap but vendors did not realise it had a brand new engine and had always been mechanically maintained by a mercedes dealership with no expense spared and the interior was still like brand new it shows 240k. Only prior repaint was one front fender that got dinged or changed and repainted because of rust.

Barry, thanks for the help. I don't think the car has been repainted but I will use a magnet to verify. I think this car is worth fixing. There is no rust anywhere else. Since I only paid $750.00 for the car I have some room to work and not be upside down. I don't think I can say that about my grey market.

Yes, sounds by your description you got a pretty good one. The inner fender patch panels are a lifesaver and really not that bad to install. If they were not available I would have had to get the metal cut out of a junk body with no rust and shipped to me as i live in the real rustbelt. If I lay in bed on a quiet evening you can almost hear any car parked outside rusting away. Have a good look around your front and rear rubber window surrounds for any evidence of paint on the rubber. Even a trace means it has been repainted. Many times when asking a vendor in states if car has been repainted they would quote they did not know. Nice to hear someone gets a break once in awhile. This site is the best auto related I have ever seen by far. If I need to know something it is either going to save me time or/and money to say the least. Plus the unusual is presented well. Knowing the common failure modes or weaknesses in this models design are also well presented. The common pool of knowledge is strong enough to allow individuals to learn and develop confidence in what they are doing as well. I go into perhaps too much detail as the person that I am responding to may have less knowledge than myself but the majority have more. Just hope I do not overdo it.

To repair the rust properly you will need to cut out the old 1/4 panals and install new ones.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Hattersguy, at present he says he has no rust on the quarters or outer fender lips. Just trying to get him to find out for himself if car a repaint. Far better if never repainted and damage confined to inner fender lip basically for sure. Should be able to drill out lip spot welds and insert inner patch panel if damage only a few inches into well and bulk of inner fender intact. If outer fenders are bad he is going to find out as soon as he starts working the spot welds in lip area. Damage in this area common but seems to vary not only in degree but in pattern. Seems to depend on how far it has gone of course as beyond a certain point one should have at least lower quarter panels at about 40.00 apiece from the danish producer. They go from the tailight to the passenger door with a wraparound of the rear door post incorparated in the pressing. Top seam is hidden by the trim strip 1/2 way up the fender. But suspect you know this. Biggest fear to me would be for complete rear wells to be rotten. Never saw one myself on a 123 but suspect it's out there. He of course at any point could consult a body shop but prior to that should establish how much rust and how far it has spread. Plus location of course before pursuing anything. I just measured an inner fender danish patch. If the inner well is solid before going in more than 51/2 inches from the fender lip. It will do quite well. Inner patch does complete outer circumferance of inner well. Just trying to help a little keeping in mind the overall value of car. Like mechanical stuff you can also have a money pit with body stuff. You just seem to feel better about your car if you do not stuff fibrefill into holes. The more he finds out the more he is in control.

Sorry I miss read the first post.

Well my honest no bs view is this:
If you cannot do this yourself, por15 the rust and patch it up.

I bet if you dropped that car off at a body shop the bill would go over $3k real fast. Buy a rust free car.

I also don't think that is the only rotted area, only one spot doesn't rot out. Their is more rust somewhere.

If you can do it yourself, start cutting and you could probably get rust free panals from a junkyard.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Hattersguy you are basically right. When the inner fenders are starting to go usually the outer quarters are affected. But have found all rust problems and patterns vary greatly from region to region in the states. I live in an extreme rust belt area. Mercedes was always known to be a rustprone vehicle this far north. (eastern canada). Sometimes upper panels are damaged and floor and undercarrage are perfect. One I saw had a perfect topside but window seal leaks over the years had finished the floor. Best ideal of course as you suggested is to get a totally rust free example but not always practical.Worst example was a car we went and saw in maryland. Think it was the car they used for the rust commercial years ago as could almost see the beady red eyes looking out through the holes in the body. Advertized as museum piece. Tragic part of doing your own body repair in a proper fashion is it takes so much equipment. I have aquired and used it over the years but to buy it all now used or new would be senseless. If you are lucky enough to have a few aquaintenances that you can loan equipment from you might pull it off. But even the minumin requirements get pretty pricey unless you have another use for the mig welders, compressors, sandblasters and all the related goodies. But on the other hand this is a do it yourself type of format and there is more than one way to skin a cat. I will always try to encourage guys to try things. A lot of forum members suggest you have to start someplace and they are right. Thinking things like using screws or pop rivets to fasten replacement metal temporarily and taking car to somebody with a mig welder. We all like our old cars but to pay other people to do all kinds of things on them would make them impractical. I think you would agree. Because of the exchange rate a friend of mine usually has a few american cars from the northern states under contract restoration at any given time at his shop. Rates here are quite low as the cost of living is relatively low in this area of the country. Seems like forces are at play to deny the average young guy a decent lifestyle though. There were 1-2 123 diesels here three years ago. Now we have 14-16 in our immediate area not counting the three I own. Locals car buffs like myself think may hit twenty five this year. (another thought is to clean up area as much as possible and use resin and fibreglass cloth or mat in the area with holes. Pretty cheap repair and anyone can do it. Just do not use normal body fill as it is porus and absorbs water. The stranded type fillers are waterproof.)

You are right cars rust in different places. My parts 420SEL was rusted in some strange areas! The metal strip between the windows on the rear doors? How the heck does that thing rot through?

My solution is this:
a. By a rust free car and keep it clean by washing it and hope for the best. IE to delay the rust long enough to get your money's worth out of it.

b. Have a nice one for the salt free months and another for the salty months.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Wow this post got more attention than I expected. Let me fill in some blanks. This car came from Kentucky. Now since I can't find anyone to do a free carfax I don't know the whole history. Upon inspection the only rust is in the rear wheel well, about 1/3 of the well and the rest goes to the well inside the trunk. The otherside of the trunk is clean. No rust in the spare tire area either. We inspected the underbody and no problems. The car has not been repainted, the color is cream and still shines. There is no rust behind the battery. Everything works except the stock Becker radio. When I get a chance I will post some pictures. My mechanic said he will cut out a well from a junk MB and weld it in. no more than $200.00 I'm guessing. Guys thanks for all the help, I believe this is the best fourm and MB-123 's are the best car ever built.

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1985 300D Gray Market 208K
1985 300D 145K

You seem to have found a good solution. Plus clarified the location a little more.(was not where I thought) One of my 123s seems to have had water in the trunk. Probably is leaking rear rubber window seal I imagine. Created rust in the trunk and lower rear portion of wheel well. If that turns out to be the case I will put small drain hole in well until I locate and repair the leak. I just find leaks by spreading newspaper in area and using garden hose if not obvious. Guess will have to hold off on my 500.00 offer for your rusty old car now. Excuse the lengths of my posts. Did not want to get into argument with hattersguy as already have one wife. (FYI benzboy 8 is offering carfaxes on a thread just a few above yours)

Argument?

Were cool just a little debating.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

I know that hattersguy, thanks.