apart from a relay it could be the flasher itself. I know american cars have flashers to make the lights flash but I'm not sure if the benz has them.
The flasher would probbaly be a round relay looking item. try to follow the clicking noise when the lights are flashing and when you find that check for proper functionality.
Sometimes the culprit can be a faulty bulb. I had a bulb that would work intermittently on and off but would sometimes not work at all. I changed the bulb and its been fine since. though the bulb I changed was for a brake light on my car....
Hope that helps you a bit.
Metallic Black (Blue Flaked) on Parchment
Black Grille Insert
17" AMG Monoblocks or EVO II's
Click here to Go To My 300CE Page