Never had a problem with mine before, or at least never noticed. Had a friend notice for me about 2 weeks ago. I was figuring either the strip in the corner, or the windshield. Guess Ill check the 3rd brake light

 

It comes in a tube and it's designed for use when installing weatherstrip. It's a black tube and is called weatherstrip and gasket maker. We've been through some more nasty rain storms with no leaking too.