I believe there was some issue with the front differential and an O ring being pressed in incorrectly during manufacturing, or something like that where others had problems.
I remember I had a lot of oil/gunk sitting under the front diff, on the top of the metal pan. I replaced my front diff fluid about 30K miles ago and all seems okay. I think some of that oil may be coming down from the oil housing gasket that is the original part at 120,000 miles.....
I gotta get under there and do some work when it warms up......replace fluids on front and rear diffs, manual tranny and transfer case.
2008 335xi - 6MT - BMS JB4 G5i - BMS DCI - BMS OCC - BMS WW Meth - Spec Stage 2+ - Spec SMFW - 19" MVR Magnum's - KW V1's - TMS 12.5+20mm Spacers