Some time ago I spoke with the owner of a transmission repair shop that had been in business for 20+ years. They specialized in transmissions for European vehicles. His position was there is no such thing as lifetime transmission fluid and recommend changing fluid at least every 100,000 miles. He was clear to only use the fluid recommended by BMW or fluid from the transmission maker as it was part of the transmission design. For the diyer He recommended draining and refilling the trans and driving for 25 or more miles and then change it again. That draining the transmission doesn't drain the torque converter. That one draining leaves too much of old trans fluid in the new fluid. I didn't ask about flushing the transmission.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas