Kevin,

I picked up an '82 300D while stationed in Germany in 1985. The Mercedes dealership in Kaiserslautern told me the car would go AT LEAST 500,000km (~310,000 miles) before ever having to do anything to the engine if the oil was changed regularly and the 25,000km service was done. Mine has 277,000 miles on it and it's still going strong.

They are good cars if you take care of them.

Don