I need to remove the windows for a couple reasons. Namely trim clips and headliner both need to be replaced. The gasket is 44 years old. It's the kind with the round rubber expander (whatever it's called) that spreads the gasket apart to form the seal. I have visions of this round rubber breaking into one inch chunks as I remove it. Can this gasket be reused at its age? Has anyone done this? Is it possible? Should I just commit myself to getting a new gasket??

I pulled the rear window out of my 69 notchback recently. I didn't try to save the gasket and cut on it. When the window came out, it had black mastic on the bottom edge. The mastic may make it slightly harder to save your old gasket, but, what the heck, it's worth a try. Maybe you can lube the round rubber part with dish soap as you go. In my case the round rubber stayed together, and the main gasket was in pretty fair condition for its age. If I had made an effort, I believe I might have saved the old gasket without cutting on it, but I had already bought a new one.

For tools, I'd use wood, not metal. Any chip or damage to the edge of the glass is bad since it is tempered, meaning it is unstable if any defect is present.

If you don't replace the gasket, you will hate yorself in the morning. The old gasket will not seal right ans probably tear when installing.

Before putting the glass back in, push gasket in place and test fit your window trim. This will verify correctness of the new clips. A lot of times the new clips are so tight the trim won't go on and they must be bent slightly away from body to reduce tension. You don't want to find out there is a problem with that with the glass in.

Another vote for replacing gasket.