My clearance lights have a sort of O-ring around the white base that is
supposed to help seal the snap/push on red/amber cover.
Upon close inspection I discovered that they actually have a built in drain
notch on one side.
Apparently the morons who installed mine paid absolutely no attention
to this drain detail. About half of mine are mounted with the drain notch
UP and the rest with the notch facing Down
Since the notch is part of the base which is nicely caulked and screwed to
my trailer, turning the offending marker lights over would be a real PIA.
I've just left them as is for now. So far they have not filled up with
water but now that you mention it, I have a small leak in my rear bathroom
window. There are 3 marker lights above it. I better go check-- I bet that's
where the water is getting in and not the window itself.