Light fixture, uhoh.

[imfignewton]

You might want to remove the light again and clean the silicone off the gasket, then reinstall the gasket without the silicone. Some times the silicone will make the gasket pinch and cause water to come in. After reinstalling the gasket submerge the light in the water and see if air bubbles are coming up for a water tight fit. Do not use the light if there is water in it. Hope this helps.

[waste]

The gasket may have dry rotted (- - a little strange in a submerged peice of equipment, but it does happen) -- pull it back out and see if you need a new gasket.