A common reassembly error do it yourself homeowner's make is that they try to wrap the lens gasket around the metal fixture and the glass lens (the thin metal lip where the glass sits on the fixture) don't do that. The gasket ONLY goes around the glass lens, then the lens sits on top of the metal fixture and you then secure it with the clamp, you will notice an o-ring type protrusion on the rubber gasket (both sides) this is also represented on the metal fixture by an indentation around the perimeter of the fixture (you mentioned an area you thought was for an o-ring on the light fixture) there should be (6) metal brackets around the light face ring ( they are the loose hanging small things hanging from the face ring ) that the wire ring clamp sits on prior to tightening, if one of these are missing, you could be overlooking this as a reason for the leak, the ring has (6) brackets, you will not be able to properly tighten the clamp to ensure a leak free seal without (6) there is also a specific lens placement, and face ring, orientation to the fixture that eliminates difficulty when reattaching light fixture back in niche on pool wall as far as the pilot screw is concerned, and how the light reflects through the lens, if light is not to old, it may still have the label on the fixture that lines up the pilot screw hole on the face ring to the fixture, (there are various notches cut out from the fixture where the lens sits that are for pilot screw lateral movement when mounting back on pool wall) and on the lens it will say "top" on the glass, which usually lines up with pilot screw hole on face ring. So use a new lens gasket preferably, make sure you have (6) brackets for wire ring clamp, don't use any kind of lube,silicone,etc ever! it did not come from the factory with lube anywhere on it, so don't resort to quick fix solution ideas, check the cord also on back of fixture, when new, cord is usually black (or yellow depending on its age) in color, if it look's greyish and deformed, or distorted in shape from it's original condition when new, especially where it goes into fixture, consider replacing the light fixture with a new one, overall, if you reassemble it properly, and hold the light underwater and observe the gasket perimeter for bubbles, you should not see any air bubbles at all, the sealing capability of these lights is consistently reliable as far as the lens gasket area is concerned, accept when something is missing,or not installed properly, etc. I have worked on hundreds of this manufacturers light's over the year's, and rarely, if ever, have had to go back out because it leaks after i did the repair, bulb replacement,etc. On a closing side note to another observation i made relates to mention of removal of the fixture completely, if attempting this remember, DO NOT! pull the electrical cord through the conduit without enough length of nylon string, or fish tape tool attached to the cord so it can be pulled back through the conduit later, if you pull the cord through with no way of pulling it back to it's original position,or have no way of pulling a new fixture's cord through the conduit, you will be sorry, there aren't to many thing's that can feel worse than finding out the hard way you cant push the cord through 50-100' conduit run. Now to the powers that be, I am aware of the concerns you have with my various violations of website protocol, and will make adjustment's accordingly in the future.