Brake Light problems of the 2011 Mercedes Benz ML350

The back gate lights on Ml350 stopped working. According to mercedes dealership, the back light(brake lights) assemblies are all corroded and need to be replaced. I asked how is this possible and they stated that they didn't know and that there was no water damage. I have also had front light issues as well, with bulbs burning out frequently. The light assembly wiring is defective. Mercedes dealership is having me pay to replace the light assemblies even though this must be some sort of defect.

Rear left brake light keep failing, the bulb is fine. Have to take out socket and put it back in, this keeps happening over and over. Was told the hole light assembly needs to be replaced. No one can seem to say why this keep happening. This can happen at any time in motion, on the highway, turning.