I’ve been down this road...first, is your leak due to corrosion of your window frames? Are they pitted and heavily corroded? If so, then you might want to bite off on the BIG job of replacing them. There are companies that make replacement fiberglass replacement frames.
Or, is the water seeping in between the glass and the frame?
More often than not, especially in a boat of this (lack of) age, it’s the bedding of the glass itself. In that case, I would uninstall the glass, clean it up, and reinstall it. I’ll have to look it up, but I think it was a black Sikaflex product I used.
If having to pull the frames and re-bed, that’s a butyl bedding compound.
You have to first identify the leak to know how to proceed, but “replacing the window” due to a leak, I think is a waste of money.
I’ve done both jobs. Pulled the fixed glass and rebed in my pilothouse. Pulled the frames and rebed in my trunk cabin sliding glass windows. The latter was a much messier and involved job which included having to replace teak walls in the affected staterooms due to water damage.