removing them reveals the parking brake shoes. If they are shot or full of cracks, they have them available here-

PeachParts FastLane Mercedes Parts Store

Replacing the shoes should restore function to the parking brake, and get that thing to THUMP when you release the brakes.

snapped_bolt

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'81 240D For now, a good place to borrow new parts
'80 300TD Probably will be put back into service!
'79 240D BACK IN SERVICE SINCE 09/16; limited use, oil leak. Guide pin r/sealed/replaced. Still a leak. Front crank seal....