Dodge Durango all over again. Dodge is very proud of the "race track" lamp on the rear of Durangos. But, it's well known in the Durango community that the lamp assembly leaks. And, when waters gets in, eventually a segment of the lamp fails. There's even a thread in one of the Durango forums where people post photos of Durangos they've seen in the wild with failed lamp segments.
Dodge has been very reluctant to replace the lamp assembly when it fails due to water ingress. It's over $1000 just for the part, so Dodge's attitude doesn't sit well with owners.
The general consensus in the Durango community is that you need to remove the lamp assembly. Then drill small holes in the bottom of the housing to make sure that moisture can drip out of the housing. And, then, you carefully seal the top of the housing where the inner and outer shells meet to keep water from getting in.
Yes, it sucks. You pay a lot of money for a nice vehicle with a cool styling feature only for it to take on water and fail. I have no idea if the Durango fix would work on a Navigator. Unfortunately, you live in typically humid part of the world, so it could be winter before the moisture disappears from your lamp assembly. Watch yours to see if any of the lamps fail. Maybe then the dealer/Lincoln/warranty provider will do something about it. Good luck!