My 95 C280 had exactly the same problem about 2 weeks ago. My mechanic told me the problem had something to do with the transmission oil leaking at some connection because the MB part was made out of plastic. I will try to find out exact name of the part that was replaced. Anyways, the white smoke coming out from under the vehicle was caused by the oil leak sprayed onto the exhaust manifold, and after highway driving with a/c on, the oil residue burning off. Cost me $390 to fix it with parts. Hope this helps.
Menlo Park, CA
1983 Porsche 944