There is a recall on this issue and you should have received 2 letters from MB-USA in that regards. Here is the info from the NHTSA website:
On April 10th, 2014, Mercedes notified ODI that it would conduct a safety recall to remedy the rear light assemblies in approximately 252,867 MY 2008 - 2011 C-Class vehicles including the C300, C350 and C63 AMG models. Each rear light assembly has separate bulbs that act as brake, tail lamp, backup and turn signal indicators. The bulbs are mounted in a "bulb carrier" which uses a common electrical ground circuit at the harness connection. According to Mercedes, oxidation due to the use of dissimilar metals on the harness and bulb carrier electrical connectors can result in increased resistance and a subsequent dimming or loss of lighting function. The heat caused by the increased resistance/oxidation can also lead to the melting of the surrounding plastic, or in some cases, present a fire hazard.
In conducting recall 14V-171, Mercedes dealers will inspect the left and right bulb carriers and harness connectors for the presence of dissimilar electrical connectors and/or evidence of related thermal damage; affected bulb carriers and/or harness connectors will be replaced free of charge. Mercedes notes that service replacement bulb carriers produced from January 2012 eliminate the dissimilar metal condition and that these bulb carriers will not require replacement.
If you have had this repaired prior to the issuing of this recall, (and assuming the work was done by an authorized MB repair facility) your MB dealer should also reimburse you for those costs.