Originally Posted by Diesel911

In post #32 is a description on how to free up a sticky/notchy U-joint.
W123 Propeller shaft vibration tears up rubber mounts, replaced nearly everything

Long before I came across that thread I had replaced the U-joint on my own drive shaft. There is 2 threads on how to do that. The U-joint is still available.
U-Joint 2005 not my thread
Can you replace the universal joints????? - PeachParts Mercedes ShopForum
My U-joint Repair thread 2011
Drive Shaft U-Joint Is Staked/Crimped In Place, Now What To Do? - PeachParts Mercedes ShopForum
My Benz World post with all of the U-joint sources.
Another U-Joint / Driveshaft Thread - Mercedes-Benz Forum

Also besides the Flex Discs in the center of each end of the drive shaft is a centering bearing. It is a tube with a seal and a bearing inside. If replacing them is not need they do need to be lubed inside.

Tightening Drive Shaft Collar Nut (coupling nut) 2011 post #40
How to replace the driveshaft support (carrier) bearing - A step by step guide - Page 3 - PeachParts Mercedes ShopForum