I have exactly the same problem as Mike (MDARR), it seem as though the pins on the bulb and slots in the holder can result in misalignment of the contacts on the back of the bulb. Talk about rank engineering.

I tried a couple of different sources for bulbs, aftermarket stores and MB dealers; my solution is to swap the bulbs around and only partially twist the bulb in the holder until it works.

As an aside does anyone know why MB couldn't use the same bulb as the rest of the industry?

Good luck,

Peter