Find BMW driveshaft and axle shaft parts, including flex discs (aka: the guibo) is a vibration dampener mounted on the back of the transmission. The flex disc acts as a buffer between the transmission's output shaft and the driveshaft leading back to the car's differential. Visual inspection is the only way to tell if the disc is beginning to wear. Cars with worn discs will notice a harsh vibration when starting from a stop and the disc should be replaced (along with the center support bearing) ASAP.
