I had the exact thing happen to my G-wagen. It turned out to be a faulty connection at the solenoid. The wire connector has some corrosion on it. I repaired it and all was well.
If the connections are OK, you should replace with a rebuilt unit from Bosch.
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM