Sounds like the trans needs to come out and the clutch replaced! This is normal wear & tear on lining. No adjustments on this clutch system other than freeplay at master cylinder.

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MERCEDES BENZ MASTER GUILD TECHNICIAN (6 TIMES)
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 16V ITS SCCA racecar