Also known as a rubber donut, the job of the flex disc coupling is to absorb driveline shunts and dampen any annoying vibrations. Positioned between the driveshaft and gearbox, over time the rubber naturally begins to degrade, and is exacerbated by the forces sent through the driveline. This issue can be more prevalent on M cars, which output more torque and are generally driven harder. We offer this quality replacement flex disc from Germany's Febi-Bilstein.