Note that I was commenting on replacing the Lexan piece that is screwed down onto the teak framing on the Ericsons prior to the factory going with alloy hatches.
I replaced the four Lexan fixed ports on our Olson -- they are frame-less and held down on a bed of sealant with screws.
If you have an alloy frame hatch, you might want to contact the hatch builder for the best way to replace the lens. I know that Lewmar has a tech bulletin on the subject, for instance.
Best,
Loren