When mine were changed back in July, I was told that they were sending the defective ones back for investigation, and that they had improved the inspection process following the welding of the plastic parts, to ensure that the upper seam was sealed properly.
The lights need to be vented, to deal with pressure changes, but I think that the venting may be inadequate, as it seems to rely on natural leakage around the welded seam (there's no visible vent hole I could see). My theory as to what may be happening is this:
1. The lights warm up during the day, and air is expelled from inside as the pressure equalises.
2. Rain or dew collects around the upper seam area, and as the inside of the lights cool down the pressure reduction internally draws moisture in.
3. Some of the moisture then condenses on the coldest part of the lights, the visible outside facing part.
4. When the lights warm up again the next day, not enough heat reaches the outside face to evaporate the water, so it stays there.
5. As this cycle repeats, more and more water collects, and the chance of the outside face of the light getting warm enough to evaporate the drops of water decreases, resulting in a permanent problem.
I think the fix might be to remove the lights, put them somewhere to thoroughly dry out, then try to seal up the welded joint around the top and sides. It might also be an idea to drill a small vent hole, like those on aircraft internal glazing, for the same reason, to allow the pressure to equalise quickly. Only needs to be tiny, perhaps around 1mm in diameter, located somewhere out of sight and in a place where water is unlikely to ever reach.
