Since the typical 240D gets 26-30mpg seems logical the 220D would get about 28-34.

And the usual parts needed are generic and easy to find... alternator, starter, water pump, glow plugs, injectors, tie rods, brakes, etc. There are very few esoteric parts aside from the start knob system on the 220D at all.

Rare parts assumption for 220D 1969 Benz is purely psychological. Essentially its the same car as 1976 240D. I drove a 1973 MB 6 cyl up until just a few yrs ago.

Nobody worries over years of age with Vintage MB's. Instead they just pick a series and model they'd like to own and then judge whats available on the market by its condition.