I'm not sure this will help in your case, so last choice if nothing else works (and disassembly is not possible):
I once managed to fix a supposedly "sealed" camera light that developed condensation after being used in the rain to film a wedding (the photographer was standing outside, waiting for the couple to emerge from the church after an evening wedding) by drilling a small vent hole, which I later plugged with...wait for it...kneaded beeswax (the kneading keeps the beeswax from flaking and makes it moldable).
The moisture evaporated quickly once air could circulate and it worked very well thereafter. When the lens fogged one later time in similar circumstances, it was a simple matter to remove the beeswax by turning the light upside down and picking it out with a cocktail toothpick before resealing again.
Just a thought. Last resort and all that.
Best,
Dan.(...who likes parenthetical asides)