I replaced over this winter. According to what I gathered the older car got a smaller tranny seal then the newer ones. I have a 07 e92 and it started leaking when I moved to connecticut. Because of the temp change the seal actually got smaller as it got cold. My car had 53k miles before I replaced it, but since i was down their i also replace the pan/filter and fluid. My cost for everything was about $350.
STETT CAI, STETT CP w/ HKS BOV, BSH OCC, P3 Vent Gauge, ECS CF Strut Bar, & JB4