I will be doing the same job in about 2 weeks (waiting for room in inside storage for the boat to be moved into before removing ports).
I asked the customer service people at PSC, who told me the following:
Pull out the gasket (you will need to replace it). Underneath is a metal plate holding the glass in place. You can unscrew the plate and get the glass out.
The glass is laminated (car windshield type) safety glass, and can be duplicated by a local glass place.
I'm not sure about the gasket. I'll have to get one out to see the profile. However, I'm sure that I'll be able to find something that fits.