This is an EXCELLENT post on DIY transmission fluid changes for the e90 BMW frame! I had the transmission fluid changed with the Royal Purple Synchromax on my 6MT car and the results were instantaneous. The shifts are smoother than the past, and the transition from the gears is more predictable (due to the fresh oil). I highly recommend this task on all yall's car.
I can see on an auto tranny how the transmission fluid can last for 100K miles, but for those of us with the 6MT, this is highly unlikely, since we go through the gears differently, especially in high traffic areas.
This is one of the best posts I've seen on this forum!