Replace the flex disc if it is cracked. It sits between the driveshaft end of the trans and differential. In the center of the driveshaft is the center support bearing and bushing. The UV joint is between the two halves of the driveshaft.

You don't have to lower the exhaust on most mercedes to do the flex discs btw. You can just unbolt the front and rear flex disc and slide the driveshaft out and wiggle it. Make sure you mark with a marker where the driveshaft was in position at. Otherwise you could throw it out of balance and have a nasty vibration.