I'm helping a friend fix up an 81 air cooled Westy.

The air cooled motor was running but leaking oil big-time near the
rear of the van.  (and #1 and #2  had about 65-70 PSI compression, #3
and #4 were about 125)

The wonderful fan on the alternator was kicking stinky oily air into
the passenger compartment.

What usually leaks oil on these beasts?

Pushrod tubes?
Rear crank seal?  (rear of van, front of engine)
Oil pump seal?
Oil cooler?
Engine case?
all of the above?

We pulled the engine, this is what it looks like after pulling all
the tin etc. off.  Notice how the engine carrier has little pools of
oil..

http://www.californiavan.com/95altima/81westy.jpg