I just purchased an '81 240D not too long ago, and just recently noticed that there is some leakage of oil on the TOP of the engine, where the hose comes in from the air filter. So I opened up the air filter and, sure enough, there is some oil in there too! I'm hoping that this doesn't mean that I have a blow-by problem and need to rebuild/replace my engine. Are there other options as to what I could be looking at?