VERY COMMON- at least here in Oregon it is.

The 203, 211, and ( i think ) 209 vehicles with sliding roofs have a defective surround seal around the frame tray. There is a dealer technical bulletin for this very complaint.
When the roof tray is dropped you'll see a tiny thin white seal around the frame tray -that's all the seal there is to keep water out of your vehicles interior.
I've probably installed the updated seal on twenty C-classes and a small handfull of the new body style E-class.

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