It is certainly not as common as differentials, but it happens. I know a poor guy in Canada who's currently looking for a deal on a transmission. He got the vehicle used, and shortly thereafter it started slipping in 1st gear. Just like anything else, they go bad. Failures, particularly the torque converter are very very common on the TDV6, two major issues, the design is different on the torque converter on those models, and it seems coolant contamination is quite common. Any water in the system, and the they are kaput. I've had several calls from dealers looking for them.