I am the owner of a 1981 300TD. I love it but I've become aware that the engine may be dying on me.

I have the opportunity to buy a '88 420SEL with around 80,000 miles on it.

What should I be looking for when inspecting the car? Troublesome areas? Prime places for rust?

hey Shawn -
I've had an 88 420sel for about 10 years now - truly a great car with a smooth engine. This particular engine has a MAJOR problem with the timing chain rails. They should be changed at 100,000, but with the age of that car I would make sure they've been changed or do it immediately. People tend to shy away from lower mileage examples because Benz's seem to almost age more without use than they do with daily driving. Oh, and about the timing chain - mine went out at 40,000 miles, so seriously - get it changed. It's an expensive fix if not cared for.
Good luck!
Peter
88 420sel
88 300e