Lifetime trans fluid? Yea right - he didn't want to deal w/you.. They use synthetic oil in the engines, (I know "air & fuel gets in there" blah, blah) They also use synthetic trans & diff fluids - but they do rec. changing them. BMW uses Castrol full syns in trans & diffs. (they use to use Valvoline but had a falling out with them over price variances) Both are sold under the BMW brand name. Do your trans & diff fluid changes every two years. These fluids do break down over time also so don't buy into the "lifetime pitch". As they'll tell you at breakdown time "Well son you ended it's lifetime, that'll be $$$$$$$$$$$"