Tom,
My guess is the case instead of being vented to the atmosphere has a vacuum
line to burn off oil vapors.
Eck

-

>On Sat, 1 May 1999, Eckie Prater wrote:
>>> My 82 air cooled had the same symptoms as above.
>> I think it is one of the reasons the PO wanted to sell it.
>> It had the tune up and a Petronics point replace module installed.
>> Guess what?  If the dip stick was just a little loose in the dip tube
>> air sucked into the engine case.  Ran like a big vacuum leak.
>> If you push the dip stick in to the seal, problem solved.