Glass shop trying to tell me new windshield seal will leak?

[Destructo]

I am having a new windshield put in my 85 K10 because the seal leaks and its cost some chips and being its not very expensive i'm just gonna have a new one put in. So I told them I wanted a new gasket and lock strip because mine is 20 years old, I get home and theres a message and their trying to tell me I shouldn't need a new gasket, because the new one will likely be more than likely leak worse than the old one?

I think something aint right here, since when did 20 year old rubber seal better than new rubber?

I'm gonna tell them to put the new one in anyway and if it leaks i'll bring it back and make them fix it lol.