It sounds like yours may be the same kind of mounting as mine. There is an aluminum frame through bolted to the cabin. The lens sits in the frame with a gasket material behind it and then the rubber gasket/spline is pressed into a grove around the aluminum frame and overlaps the lens holding and sealing it. The picture below isn't my boat but this is the type of window I have.

I couldn't find the gasket material so when I replaced the acrylic I bonded it in. I thoroughly cleaned the aluminum frame, gave it an alcohol wipe and then bonded the acrylic lens in place using Sikaflex 295UV. You need to prime the acrylic lens with Sika primer 209N which is quite expensive but the 295UV is fairly cheap. The windows are well sealed and appear to be very well bonded. You need to mask everything off because you need to make sure you get full coverage and you end up with squeeze out. The primer is black so make sure you mask the acrylic before applying the primer.