Same thing happened to mine about 3 week ago. Had to overhaul the transmission. Look for a reputable company that had experience on Mercedes units. Only thing a dealer will do is a Mercedes exchange for about $4500. Had mine rebuilt for $1500.
One question - is there an adjustment for pressure on the exterior of the transmission. Sometimes mine now shifts with a little hesitation expecially 2-3 and 3-4. Will only do it at part throttle, never at full throttle.
370K + SOLD
1952 220B Cabriolet
39K kilometers + SOLD