You do not need a new seal...becasue GM applied the sealant AFTER the glass was installed.

What I wrote in POST #35 ( paragraph 2) 'says' it all. If you use the #M 8509...you WILL regret it. Just give it time. And if you do use it and it works...then GREAT. But I stand behind what I wrote and I would toss the 8509 off to the side for this specific purpose.

If I am not mistaken 'JohnZ' posted archive GM photos of the actual process of GM adding the sealant. In the pinch weld and also between the glass and the windshield itself.

DUB

 

Regarding the sealing the windshield, I could not find JohnZ pictures, but I did find other pictures in this post. Following the 63 pictures, I applied a bunch more 8509 in the gap between the upper seal and the windshield rubber gasket, and by filling up the gap, it sealed just fine. DUB, to your point, 8509 is really messy. Since I need to re-do it anyway, I have a chance to use the other product.

Sealing the glass to the gasket was trivial - this product hardened, no issue.

I think I am doomed to learn everything the hard way. Now - apparently I had set some of the clips that hold the modeling too low in the channel. Damn, Figured If I put them all back in the holes they cam out of, they would just work. Several of them just do not clip. I did not check them to make sure they were all the same and I did not measure distance between the rim and the hold for every clip. Live and learn.

 

My last word on windshield install - from my multiple trial and error experiences.

This last time around I repainted the windshield mounting area - primed, color, and clear. Note the Clear we get in California takes several weeks to a month to get hard. I would not advise installing the trim until the clear coat is good and hard. Also, as long as the clips are all installed to the correct height, put the trim on after the windshield is in and the Glass to rubber seal "sealant" has been applied.

Regarding the sealer between the chassis pinch weld and the rubber seal - what worked best for me.
0. Mask off the dash panel right up to the inside facing pinch weld, but do not mask the pinch weld itself. Install all the clips and verify correct height. If they are too low or too high, drill an new hole 1/4inch to the side of the old hole at the correct height. Seal up the old hole. I found the 5/8inch is the correct distance from the edge of the body to the center of the hole. I also used the US made clips from Paragon for the trip. They have staged clip points.
1. install the rubber seal on the windshield as described
2. insert the rope as described
3. put a 1/4 inch bead of the 8509 or the equivalent that Dub recommends on the outside facing chassis pinch weld. See the pictures of the 1963.
4. center the windshield in place make sure the rubber is correctly seated inside the clips, on top of the bead of sealant. Make sure it is centered.
5. Put on some the blue gloves and execute the rope trick. Note as the inner portion of the seal is pulling around the pinch weld by the rope, the sealant is scraped off the inside part of the rubber seal and is deposited exactly where it needs to be. There is still clean up on the inside, but it is not too bad. This process gave me a solid windshield gasket to chassis seal and is what I recommend.
6. prior to installing the windshield trim, apply the glass to rubber polly sealant by lifting the outer edge of the rubber and squirting sealant into the slot at the base of the glass.