Sorry to have missed this until now. There are a few things required to seal the light. The gasket is the way to seal the lens to the body, all 3 must be in good shape to fully seal the unit - so check the lens and the sealing area on the light casing (make sure they have clean, flat surfaces). The other part of the seal is the ring or screws that hold the lens, gasket and casing TIGHTLY together, your problem could be as simple as stripped threads on the tightening bolt(s). Also make sure that the casing doesn't have any 'pinholes'. One other thing, the 'rib' on the gasket goes against the casing. Hope this is enough to help you seal the light.