Ok this is for a W126 so take it with a grain of salt, although it should be similer on a W124.
Unbolt the driveshaft from the flex disc and push it back a bit. Then unbolt the flex disc from trans. The flex disc should drop right out after that. They stick sometimes and may need a whack to help it along.

Just repeat the process to install. MB gives a torque spec but I just made mine tight since I didn't have a torque wrench handy.

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