Just to add my $.02 to the discussion on the use of synthetic oils in 
air-cooled
engines, I recall reading a tech note from Gene Berg that recommended not 
using
using it.  As I recall his data determined that the synthetic oil rejected 
more heat
than regular oil and therefore did not transport as much heat from the 
moving
parts(crank/crankbearings, etc.) to the oil cooler.  His bottom line was 
that the engine
tended to run hotter with synthetics.  Just another data point.

Charles Armstrong
'70 Bus