[matthewmilbut]

I have a very expensive watch. I once went swimming and forgot to take it off before diving in, water condensation got inside of it. I called the jewelers and their advice was to remove the watch cover and sit it by a lamp with the open side up so the water can evaporate. Worked like a charm. Getting the back off was the hardest part.
So in theory, how about removing the taillight unplugging the light assembly and leaving it sit out as I did with my watch? Also, if needed, at the same time you could fix a repair with the gasket with some silicone as described above.