The Tubes on the Flex Disc go into recesses in the Yoke with sort of a light press fit and then they rust in place.
In My case they were also frustrating to remove but I kept working them and eventually they came loose. Should be info on that in them DIY Repair Links.
Penatrating Oil can help. But, don't get Oil on the New Flex Discs.
You also need to lossen the Collar Nut on the Drive Shaft.
Repair Links
DIY Links by Parts Category - PeachParts Mercedes ShopForum
PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles
Once the Flex Disc is loose there is a Pin that centers each end that is more than 1 Inch long.