I have om603 turbo with almost 250k miles as daily driver.
I like it, it's not fast, but it's just enough to live in a big city. It's fast compared to om617 for sure.
1. Take off valve cover and check timing, then check timing relative to injection pump. Check chain slack if any.
2. Turbo seals like to go bad and smoke, I replaced the whole turbo on the cheap and it's been fine.
3. EGR delete is a good thing to do.
4. Blowby...a little is ok. It likes to spit a bit of oil around turbo, that's normal.
5. Delivery valve seals, sooner or later, plus make sure the hard lines from IP to injectors have all their plastic holders. There's a lot of vibration and they are a must!
6. Other than that, as others mentioned, belt and belt tensioner is very common failure point.
Usually these engines are really good, I have the #14 head and no issues even when car got to 110 degrees.
Typically your transmission or axle shafts will go first rather than this engine
If you are getting this car, I highly recommend doing LiquiMoly Engine Flush right before first oil change.
Then, of course, Diesel Purge with all new filters, as you probably know
It really makes a huge difference for city drivers