I had this happen to mine, does seem to be a common thing. I found that the water was not in the light itself, but in between the two layers of the lens. I pulled the light out. Sealed the bulb hole, chilled the unit in the fridg. and submerged the unit in hot water. Found bubbles coming from the top section of the two layers.
It would appear that the two layers were not sealed at the top, so that, when the car was washed, cooling the light sucked water into the space, between them.
My fix was to run Super glue along the joint, between the two layers. The glue sealed the joint. That was four years ago, no condensation since.
Harvey.
