Did you happen to notice if the starter motor problem emerged shortly after you replaced the battery? If so, double check your battery cables for tightness. I have experienced a number of head scratching electrical problems with later model MB's all because of a loose connection. Some time back I worked on a 400E that cranked just fine but it would not start, cause: loose negative cable at the battery. One would think, and I did, that high current demand by the starter motor could not be attributed to a loose cable otherwise motor speed is affected, boy was I surprised.

Prior to exploring an electrical complaint I have discovered that time can be saved by checking the battery connections for tightness. This goes without saying for the late model vehicles because they use numerous computers.