Doing 15,000 mile oil changes wouldn't have been a problem; short trips and never warming it up completely would be much more worth worrying about.

Seafoam and similar solvent type cleaners can be very harsh on seals and plastic parts. Not recommended.

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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