we've got a problem with one of the latest Vauxhall petrol engine's doing this due to a faulty one way valve in the cam cover that connects via a pipe to the inlet plenum. The vacuum is strong enuff to suck the engine oil up into the inlet and create a Batman style smoke screen....plus you are totaly unable to remove the oil filler with engine running. Dunno if a old BM has a similer one way vacuum valve set up?