Well, even though this discussion is a little old, it is a current problem for me. I have a 1992 Mosler cb40. Mosler case, not vw. Have original paperwork from when it was test run at factory. It has a 1 inch hole in the top where a breather should be, I think. No threaded holes for bolts. Also was not drilled for a dip stick. I think it was supposed to have some kind of breather/filler combo I’ve read about, but I have never seen one if it exists. No matter what I have tried, I get a lot of oil along with the crankcase pressure out of the hole. The engine case is only supposed to have 1.25 quarts oil inside, with this small amount,I feel a loss of any is unacceptable. My last attempt was a check valve in the hole at the top, with a hose to a vented separator, draining out the bottom thru a hose to the rear bottom of the crankcase. Within one minute of running, there was oil pushing out of the air filter on top of the catch/separator can. There’s got to be an easier way to vent the crank case without losing oil.