Need a new o-ring in the chargepipe. I pulled them out to measure and ordered ones that were a tiny bit fatter, but I can't remember what size. They are not available from BMW separately. I ordered a bag of them from McMaster-Carr.
It could also be oil from an oil filter housing leak making its way down there, but that usually cakes dirt on the front of the motor.
E92 335i/6MT Dinan Stage 3: intercooler, oil cooler, intake, flash, exhaust, LW dual-mass flywheel.
Vishnu PWM methanol custom trunk mount, Diffsonline 3-clutch Salisbury custom diff, Ohlins Road and Track coilovers, Vorshlag camber plates, much more...
E28 M5 w/ buncha stuff, R171 SLK350