I think $6000 is way too much for that car. I just looked it up at kbb.com and got $4600 for retail. That's if it's perfect and you're buying it from a dealer. Trade-in value is $2000 according to kbb.com.
I just paid $5900 for my 300SD with 117000 miles from a used car dealer, and I'm starting to think I got ripped off, cause my transmission needed rebuilding about 200 miles after I bought it! I'm really wishing I would've bought from a private party. It's always cheaper to eliminate the middle man.
If you haven't owned one before, you'll soon find out that you get a lot of car for your money with an old Mercedes.
I'm not a mechanic, but I would say one thing to watch out for is rust.
Santa Barbara, CA