Originally Posted by Blast Chamber

Does the car still have the original OEM battery? If so, it is 6 years old, and there have been cases of older batteries with lower voltage causing weird symptoms in the Mercedes electronic systems.

I realize this is thin and is just a WAG on my part, but if you are soon due for a new battery anyway it may be worth a try. I'll be replacing my OEM battery next week even though I'm currently having no problems.