I have the same problem with my 1998 C230. It is at the dealer for the 4th time. They replaced the valve body and controller the first time, rebuilt the trans the second time, and "couldn't find the problem" the next 2 times. It is sitting at the dealer with an open ticket, preventing the warranty from closing. I bought the Heritage warranty from the dealer a month ago to cover any problems, now it looks like they may not cover it as well as it needs!!! I am currently waiting for word back from the Shop Manager, who is talking to the regional rep. Next step will be the dealer General Manager, then the MB rep, then MBUSA, California Bureau of automotive repair, etc. You DON'T want to get stuck with a transmission bill, or on 'goodwill' for repair.
These threads may give more info:
MB Doc - diagnostic champ!
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E