must replace gasket on windshield

It depends on what gasket you are talking about. On our 2001 GB the outer rubber gasket seal was attached to the windshield glass with two sided tape. There was no adhesive on the fiberglass side. This outer gasket strip had come loose in a few places. I peeled the gasket off (it's about thirty feet long), cleaned it up, and reinstalled it using a generous amount of black Dynaflex 230 from Home Depot. The windshield did not have to be removed to do this fix. I have seen some glass replacements where a seal strip is installed around the outer rim of the windshield and then the glass is then pushed into place. My GB windshield, and maybe yours, is glued to a bed of black butyl compound like a car windshield would be. I cleaned out around the glass and added some sealant where it was applied pretty thin at the factory before reattaching the outer seal. There is a similar strip of rubber gasket down the center pillar that separates the two sides of the windshield. I ended up using a piece of it to replace a damaged section of the longer strip. It was identical in cross section. A piece of black plastic body side moulding was used to replace this center strip and bridge the gap between the glass panels. It adhered to both sides of the windshield with adhesive tape already attached. The most difficult part of the entire project was figuring out a way to reach the far upper corners of the windshield. That black caulking was also pretty messy, but water cleanup made it manageable. I did not use silicone caulk because of how difficult it is for me to work with and remove if need be after it has cured.