water leaks into brake light on spoiler

hello,

yesterday, i noticed mold growth inside the cover of the thin horizontal brake light on the spoiler. i even got a whiff of that delightful mildewy smell without having to put my nose right up to it! i have yet to attempt cleaning it up. looks like a simple job of unscrewing and wiping.

has anybody else noticed this? any way to seal it?

haven't closely investigated, but i imagine water seepage is from pressure carwashes and not rain.