Originally Posted by BMWN54tech
To be perfectly clear, all turbos will have oil on the charge side. That is what turbos do, and why catch cans exist. The question is if it is excessive oil.
The oil comes from the fact that the PCV is recirculated to the intake tube of the rear turbo pre-compressor. The oil in the charge piping dousn't come from the turbo itself, as the water jacket is on the compressor side, the oil is on the turbine side in the bearing housing. The oil is blow-by from the crankcase that will build up inside your FMIC, then reach the charge tubing and diverter valves eventually into your motor and onto the intake valves.
And catch cans don't exist to catch oil from turbos, they exist to catch and condense PCV oil-enriched vapors to prevent the blow by oil from entering the intake tract. Excessive PCV oil can be caused my a number of different things as well, ranging from a leaky check valve to issues with your piston rings being worn.