Respectfully disagree - the transmissions, at least in the W123's and older were simply not of the quality that one would expect from Mercedes. Even when perfect, they are very inefficient and sloppy shifting. We have always had an American car and a MB, and I am amazed at how much better the US transmissions work.
MB DOC is correct in his second observation. The basic design problems are compounded by a large number of fools at dealerships who don't know how to adjust them correctly. It was always a crapshoot as to whether the automatic in our beloved 300D would work better or worse after being serviced!
Falls Church VA
'86 300E 5 speed
'95 C220 (wife's car)
'98 Porsche Boxster
Past: '79 280E, '82 300D (18 yrs), '77 240D,