Hopefully you guys didn't get the SLK intermittant bulb holders... Mine is always the right rear running light. The tabs on the sockets start to loosen and make intermittant contact. If not caught early, the plastic starts to melt. Mercedes had a TSB on them and even though I had mine replaced under the recall with the new style, they are doing the same thing...

Keep in mind this is the Benz SLK I'm speaking about, just figured you can check them to see if you got another one of our "known problems"...