Seal on 3rd brake light?

I have a question , tried search but came up with nothing. I am changing my 3rd brake lights to LED bulbs. The skinny , black rubber seal fell off the lens. My question is...
Does the seal sit in the hole on the actual assembly on the truck or does the seal sit on the little tiny edge on the red lens itself? I've tried to put it on the lens but it doesn't want to stay and seems to be a little short on coming and meeting up with itself. Tks.

 

it is a little short to act as a drain im guessing. mine was the same when I swapped in led's

 

Did you try to wrap it on the lens or put it in the hole around the fixture ?