I have an '84 Westy with about 200K miles (the odometer broke in 1991 with 104K on it) on the original engine.  I never used synthetic oil and it has leaked from just about every possible orifice since I bought it.  I always seem to be one leak behind.

Me thinks that most Vanagons leak oil, and some leak more or less than others - the type of oil probably doesn't make any difference.

cheers,

Ed
'84 Westy in Syracuse