I recently bought a 73 220D. I'm no MB diesel expert or even good enough to be called an enthusiast. Consider these comments from a rank amateur.

Very fun to drive. The ride is much softer (in a good way) than my '87 TD. Pretty quick from 0-12 mph, then the world catches up and passes you by. Easy to work on in that the car is simple. (I just spent a weekend pulling parts of a car going to the junkyard.) But changing belts is a PITA. If the paint job is good, it'll be a head turner.

As to price, it's all relative.

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1987 300TD; 166,000 mi/267151 Km - had to make room for the dog
1973 220D; mileage ??????
1978 300D; 178,000