Are you seeing engine oil at the bottom of the transmission bellhousing, but none above it? If so, your rear main seal is leaking. One big culprit for a rear main failure is a defective PCV, which causes intake manifold vacuum into the crankcase.

This Elring rear main seal with flange will clear up that leak, and keep your oil inside of your engine.

For added sealing protection, VW and Audi technicians often use a little silicone to aid in the sealing process. Links to the silicone, bolts, as well as a completed kit can be found below.