I have an 87 Synchro Westy with 153,000 miles on it.  I was told the heads
had been reworked at about 120,000.  I started getting an oil pressure alarm
below 3100 rpm after the engine has warmed up.  I replaced both oil pressure
sensors, and just finished replacing the oil pump with a high volume pump
from Bus Depot.  I still got the alarm after then engine warmed up.  Bummer.

A mechanic friend of mine says that my main bearings are probably worn to the
point that there is too much clearance.  About ten years ago I rebuilt a bug
engine.  I remember having to have the case line bored.  Of course, this
required OD bearigs.  Is this common with the 2.1 Wasserboxer?  Has anyone
out there replaced the main and camshaft bearings without having to rebore
the case?  

If I do decide to rebuild, what other pitfalls should I look out for?

Maybe now is the time to look for that Subaru engine.