Windshield Removal

If the windshield has never been out before and it is worth reinstalling, I would suggest sacrificing the rubber. Use a box cutter and get the glass out intact.
Expect to find something like plumbers putty in the lower channel. Junk. That's why the leak.
If it is original rubber it will shrink up on you anyway while the glass is out. I've had old gaskets and reused them by keeping the stretched between post, then putting them in quickly.
My method of installation isn't for everyone. I go to Home Depot and get the black polyurethane roofing sealant in the tube. I glue the gaskets in. By doing this I've been able to take windshield back out and in without the gasket coming out or ever leaking.
To take glass out or put in, I use a bunch of rounded putty knives and shoe horn them.
I've even used a sander and smoothed the edge of the glass to help.
(Use respirator)
The biggest caution is not to twist the glass. It is pretty tough but won't take being twisted.