Agree that it sounds like the oil separator valve. The trouble with guessing exactly where the oil could come from is that when the valve freezes shut and pressurizes the crankcase, it can leak anywhere, such as the valve cover, or from the valve itself. The valve is a likely cause, but you just need to follow the leak up to the highest point to make sure it hasn't also caused a leak elsewhere.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue