here's an old post I wrote a few years ago. Might be of some help:
Hey Boys,
I was an auto glass installer in a prior life.
Couple things to add
1. Whether heating the seal will help depends on what is holding in the windshield. There are 2 proper methods and one bad, but common improper one. The proper methods are Urethane caulk and butyl tape. The bad one is silicone caulk. BAD, VERY BAD!!Heat will only help if it is butyl tape. You will know its tape if from the INSIDE of the windshield, when you stick something into it (i.e. wire, nail etc.) it has a consistancy like chewing gum. It is common to cover the tape with another sealer like silicone or urethane on the outside, so the outside surface is not a good indicator. Tape is cut with a hot knife in a glass shop, and it literally cuts like butter. But, like I said, it is normally top coated with urethane, which doesn't react much to heat. SO, for the do it yourselfer, your best bet is piano wire. Piano wire will cut anything used to install a windshield. You could swing by you local glass shop, and I'm sure they would sell you several feet for a few bucks. Glass shop wire is not actual piano wire anymore, but rather a similar wire with abrasives imbedded in it.
Rather than vise grips to hold the wire, a better method is to drill a thru the middle (the short way) of two 6" ish pieces of old broom handle or similar round object. You thread the wire thru the holes, and twist it off, so you end up with a handle like the pull handle on a lawn mower, at each end. You wire ONE end as I descibed, then, push the other end thru from the inside of the car out, in an upper corner with needle nose, as described above. pull it thru on the outside by grabbing the end with the needle nose and pull thru. THEN twist up that end like the first. It is easiest to cut out the windshield with 2 people, one in and one outside the car. If you find that as you cut, the seal sticks back together, then you have a seal that is at least based on a strip of butyl tape. You simply need to apply outward pressure as you cut initially. Once you have cut far enough that there is a decent gap between the winshield and the tape bed, just stick objects in like a screw driver or such to prevent the winshield from making contact with the tape untill you have cut the whole thing.
Also, be very careful of your dash as you cut. I ALWAYS put a piece of smooth sheet metal about 18" long over the dash where the dash meets the windshield, and move it along as a I cut . Any thin hard surface will do. The key is to make CERTAIN that the wire is not touching the dash as you are pulling back and forth to cut. One stroke across the dash with that wire will make an irrepairable cut. Trust me.
There are a number of other things you might want to know about this whole windshield gig, but the above should get it out fer ya. If you want to know more, just say the word. None of it is rocket science.
Chris