I have seen this problem with quite a few of the E's. We have had them repaired under warranty by the local Atlanta dealer. The solution is a mod to the contactor plate. They did this to one of our cars three times and the third one fixed it. Mercedes knows of the problems, but it is up to the professionalism of the service department to solve the problem for YOU. Thanks and good luck.
If you are in the Atl. GA area, I might be able to help.
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM