Hi David,

Agree with the comment about excess crankcase pressure. Suggestion: check to
see if the crankcase breather hoses from the vent tower to the air intake
distributor are sucked flat at 2500 rpm.

Story behind this suggestion. I acquired an abused 86 Westy Weekender.  It
was leaking engine oil out the bottom of the clutch area, had a death
rattle, and numerous other ills.  I replaced the engine with an AVP core
rebuild.  Transferred all the bits and pieces over to the new core.
Replaced every hose that needed it. Had the end play adjusted by a local
shop and they put seal in. Put everything back together, started driving and
noticed I still had engine oil dripping from the bottom of the clutch
housing.

Hmmm.  Pulled the engine, seal looked fine.  Put a new seal in.  Still
leaked.  Hmmmmm.  In desperation took it back to local garage (Fred's Garage
in Redwood City, CA)  They dropped the engine, replaced the tranny seal,
replaced the main engine seal. The mechanic noted that the seals were fine
so went looking for some other problem.  Found that the hose that connects
the  crankcase vent tower (little beer can shaped thing on the top rear of
the engine) to the air plenum (air intake distributor - black bulge top
middle of engine) was so old and soft that it was sucked closed by the
vacuum from the airbox at anything over 2000 rpm.  This effectively closed
off the crankcase vent and drove up the pressure in the crankcase, causing
oil to blow past the main seal.  Stuck a new piece of hose on and all was
wonderful.  Time to fix problem, 5 minutes.  Cost of hose, $0.50. Time to
diagnose problem - 2 hours.

Was tough to find as the hose looked fine at idle, only collapsed at higher
rpm, and since it's buried under a bunch of other stuff it is quite hard to
see the collapse.

Three cheers to Fred's for finding it.  They felt responsible for the
original seal, their mechanic pulled the tranny seal even though it was
clearly leaking engine oil, not tranny oil so they only charged me $135 for
the time it took to diagnose the problem.  My kinda garage :)

Hope that this helps,

Millo

86 Westy weekender
67 Porsche 912
00 BMW 528i
89 Chevy Pickup 1500