It is a 220D. Indeed a W115. Pre-1972/73, because it has a smaller grille and the old small sideway mirror. Bumpers look euro, headlights are US-DOT.

As far as I can see, it looks good.

The engine (if original) is a OM615 engine, produces 60HP. The diesel pump has a pneumatic governor, controlled by a vacuum created by a venturi and a butterfly valve in the intake manifold.

The IP has it own oil.

It has a oil-bath air filter.

The oil filter consists of two parts: a main filter which can be cleaned and re-used and a by-pass filter, which should be replaced.

Any reason why it hasn't run for a long time? Is it broke?

Here are some more technical facts about the 220D:

http://et.mercedes-benz-clubs.com/mediawiki/index.php/Kategorie:W114/W115/en#W_114_.2F_W_115_sedans_series_1
(scroll down to 220D).