Although I just glanced through all the posts, but I didn't see anything about pulling the bulbs and just checking the seal on it.
Seems to me that it would just be smarter to pull them out, make sure the little seals around the non-led bulbs are not torn, missing or pinched.
I'd also get my heat gun out, and very lightly (and at a distance) blow some hot, dry air into the housing until its all dried out. Reinstall the lamps and see how it does after that.
It just seems to me that the housing was open when it was probably very humid out, allowed it to get trapped inside the housing, and when it gets cold or warm outside, it starts sweating inside the housing. Drying it out completely should solve it, if the seals around the bulb holders are working properly.
Or maybe this has already been done by the dealership and that's why they are escalating the issue to corporate?