I had an intermittent light out indicator also. It would rarely come on, just enough to annoy me. Yesterday I was replacing my license plate light lenses with new ones (Mercedes P/N A 230 820 01 66; only about $10-$12 each from a Mercedes parts place). When one of the bulbs came out, the end fell off. It's like the glue holding the metal cap on the end of the bulb is all crumbling, but the wire is still coming out of the glass. I tested with an Ohmmeter, and what's left of the bulb is still good. So I think the wire was making pretty good contact with the cap, and it would almost always work. Then sometimes it wouldn't work. Every time I looked, I never could spot a light out. Hopefully that makes this mystery solved.