I'm guessing they're all the same but if pumping the pedal doesn't improve the situation, I don't think that replacing master and slave will resolve the problem. On some slaves, there is an adjustment on the actuating rod. Don't know if MB's have it but I would certainly look because it sounds as if you are not getting enough travel out of that rod. Lengthening the rod should give you more travel and a full release of the clutch.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13