After some more measuring and comparing my slave cylinder appears to be out of a 350SL. They look the same but bore diameter is 22.2 mm instead of 23.81 mm. This should make my clutch pedal harder by 7% if my calculation is correct.

W111 3.5 slave cylinders are on back order and repair kits for 350SL slave cylinders are NLA. Mine does not look that bad so I will clean it and put it back in.

Seal looks nice and supple but obviously it must have swolen as it makes the piston sticky and the spring inside does not have enough force to push it back. Is this a common problem? Is there a trick to have the "retract"?

Thanks!