BMW has used both 100,000 miles, and lifetime, recommendations for transmission fluid changes. What has changed is the application, the transmission design, the fluid, BMW's experience with fluid changes, and various extended service plans. What we don't know is how much each of those factors influenced BMW's recommendations.

The service intervals have a baseline, and then are adjusted by things such as fuel consumed. They are also using sensors that directly measure oil condition now. This is all for engine oil change intervals, more than for other fluid intervals, as I understand it.

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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