It's been 15-18 years since I put a new windshield in my 66 Hardtop. The shop supplied the windshield ($100 at the time) and I supplied the gaskets, front and rear (I wanted the cracked gasket changed on the rear window, the glass was OK). I supplied the NOS gaskets. The shop used one tube of sealer on the rear window, and four on the windshield. They said the thinner repro windshield was the problem not the gasket, but were happy I supplied NOS gaskets.
Jim