I've had a 3.0is and a 4.6is. Each had a transmission that shit itself. On the 3.0, I damaged it by spinning in the snow at full throttle, then the transmission shifted just as I got to the pavement and blew out 2nd gear. BMW quoted me $6500CAD for a new transmission. But being the cheapo I am, I called every specialty transmission place in town to try and get a better deal. When almost everyone refused to take on the repair, that should've been my que to go back to the dealer. Instead, I made a brutal mistake, and let Dot's transmission in Edmonton Alberta, convince me that they could do the work for $1500 to $2500CAD. The work took months instead of a couple weeks as promised, and cost almost $5000CAD. The truck was half decent in forward gears, but had a terrible binding when in reverse. Bottom line: unless someone has EXTENSIVE repair experience on BMW transmissions, your better of just paying the stealer.

On the 4.6, it had the terrible "bang" when it downshifted. It started to go into a 4th gear fail safe mode off and on, until eventually it stayed in 4th. It was a US vehicle with CPO warranty, so I drove 12 hours to Spokane in 4th gear. They had ordered a sensor that the Edmonton BMW dealer had diagnosed as the problem. That wasn't the problem. BMW Spokane ordered a new transmission under CPO warranty. Bottom line: As much as we all want our transmission problems to be a $200 sensor, it seems that sometimes we just have to face the reality that the problem is in the transmission, and to get it fixed right the first time, is gonna be expensive.