Windshield gasket replacment

If you are sure your glass is good enough for re-use and not going to try saving the gasket... Getting it out- even by cutting depends somewhat on how much and what kind of sealants were used on it. You should be able to pull the lock strip, then cut just the part that laps over the glass on sides and top. At that point it is still seated in the bottom, and the top and sides are laying on the gasket. As long as they didn't get much under the glass you should be able to push out on the top of the glass and it will pull away from the gasket. Now with glass angled out slightly, pull the top and sides of the gasket off the pinch weld. With bottom of gasket still on glass lift it off the car. Then get it to a safer spot and as said previously- clean ,clean,clean.

As for the leaks there are a number of places along the side that could leak. Any place a metal seam comes together should be suspect. One that took me a while to find was under the cowl drain where it joins the side panel (only accessible with fender off)