How rare is the M21 in a E34 in the States?

[Ferret]

http://en.wikipedia.org/wiki/BMW_M21

why was it phased out?

here in Europe, it is all the rage. and you routinely see 525TD with over 300 000 miles being sold here.

The M21 engine is not fitted to the 525TD/TDS - that's the M51 engine.

The M21 in an E34 makes a 524TD, which had a production run 1987-1991

If I remember correctly the 524 is a six pot diesel engine, with a cambelt, which was underpowered and not terribly reliable...