Mike,
the light is a poor design. The gasket is set in almost 1/2 inch in from the edge of the light..
Water, dirt, dust, leaves, all sorts of junk will collect in there....
Best thing is to remove the light and clean it and re install it...
You could use some silly cone but then the gasket would get damaged...
OR You could run some of that self adhesive window foam around the underside of the light and re install. That might do the trick..
Todd Z