I have a 89 300e, that I bought used with 130K on it. It is my first mercedes and like you I dwas pretty nervious about the whole thing. But my wife just had to have the car even against my better judgement.
The car now is getting ready to turn 250k. I am by no means a mechinace by trade. I enjoy working on my own cars though, and have had to replace the usual parts that go out, water pump, alt, belt tensioner, ect..
I'm pretty tight with all the local salavge yards, due to the price of mercedes parts. But I must say the car has been very good to us and even though it's older, there's a certian mistique about driving a mercedes. People just automatically think different of you because of it.
I can't say for sure but depending on the deal and the shape of the car I don't think you can go wrong