Rear window weather strip removal

I don't think I'd use any kind of sealer that would harden. If you ever had to pull the glass again, that might a problem. On a windshield or any other gasket that uses a lock strip, a different procedure can be used both removing the glass and installing it. With a lock strip setup, sometimes it's better to install the gasket, and then install the glass. There again, you need to carefully peel the rubber around the glass without breaking it. With a new gasket, that would be easier than an old stiff one. Condition of the gasket would play a deciding part on which way to install should a new gasket not be available or it's cost is out of the budget. When I install the gasket first, I first remove any slag or sharp edges on the pinch weld. You could tape the lip if you would rather, say with some friction tape or similar. I use a gooey, putty like sealer between the gasket and the pinch weld. I don't tape if I use the rope install method as it tends to bunch up and get in the way of smoothly installing the glass/gasket assembly. With a good gasket, I haven't had any problem with leaks between it and the glass. It's always been between the gasket and the frame where I've seen the leaks....or the wiper post seals! I guess it's possible though. If you could inject a small bead of non-hardening sealer on the outer lip between the glass and the gasket, that would probably work great, then install the lockstrip to seal it up tight.