So, I took advantage of a heavy rain to see from where the leak orignated on this hatch. I can tell from the weeping water that it is actually the glazing around the lens/glass, not the gasket seal.
Would the next step to be to completely cut out the glazing (seems like a silicone caulk) and then re-glaze? I'm looking on the web now for some how-to demos.
You can see from this photo (if you look closely) that the caulking is compromised around the corner.