From the looks of the pictures, and the one from the first set, you could just have a valve cover leak that's wetting the whole engine. (I did on my 300SD when I first started playing with it.)

As to the flex disc, yep, just the casting mold separation lines leaving the little bits of rubber on the edges.

Tires are consumable, I wouldn't normally consider them unless they were new, but having them this bad, I'd point them out as leverage on the price.

As to the differential leak, I would look to see where it was coming from, but off the top of my head, I'd say that the rear seal would be my first suspect, along with the drain plug. Following that, the side shaft seals can start leaking, and while they aren't expensive, I'm not sure what it takes to replace them. (getting ready to do just that on my SEC, a learning experience!)

I'm not sure on the price for it, but it does seem to be a mostly sound car.
The faults it has look like they could either be easily corrected, or possibly be something that could blow up in your face. (That seems to be the case with any vehicle, but I try to keep it in mind.)

__________________
-Josh
Testing the cheap Mercedes axiom, one bolt at a time...