The oil separator freezing up is a well known issue, made worse by short trips that don't allow the oil to burn off all of the condensation. The condensate freezes when it gets cold enough. There have been a variety of factory fixes; while they appear to have helped, I think the vehicle is still subject to this problem at times. Do a search on this site on 'oil separator freezing' and you should find quite a few posts.

Sounds like you have a good solid dealer, which will serve you well. As to whether this is the start of a slow decline, well, it isn't a new vehicle any longer. If you have an extended warranty you are in better shape, but you should expect some problems as it ages.

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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