Originally Posted by SeriousE92
Where is that film/oil coming from? Is that a problem long term and are there any fixes for it?
I haven't spent too much time under the hood of an e90, but I'd guess it could be EGR (exhaust gas recirculation) or PCV gasses. Both would be normal.
EGR systems take some exhaust gas and inject it into the inake air stream under certain conditions to reduce emissions. It contains carbon deposits that would build up over time.
PCV is positive crankcase ventilation. It releases pressure from the crankase. Instead of venting the air into the atmosphere, it injects it into the intake stream. This air also has unburned fuel and oil.