Heat will pull moisture into the housings no matter if they’re sealed or not. This usually occurs after the lamps are shut off on humid evenings.
Remove any plug that may exist, drill a small hole, or whatever in the bottom of the housings and this should cure it.
Both of my Lincoln Marks were horrible about this. After removing the 1/4" plug in the bottom of each housing I routed small air lines from each housing to the air cleaner. There has been zero drops of water ever since and the main reason for the air line was to remove heat when the lamps were on rather than condensation removal. The lamps now run cool to the touch so ergo, no moisture attraction.
I second Mr. Meehan wholeheartedly although it will never happen. Why replace a plastic stylish lamp with something that is cheap, reliable, and downright effective.