[joe_padavano]

Let's hope it's the heater core, because the alternative is not pretty. The A-body cars are very susceptible to rust in the pinchweld area where the windshield and back window are bonded to the body. If you're lucky, it's just surface rust that has caused the butyl rubber seal to lose adhesion. More likely is that there is a rust hole. Unfortunately, the only way to correctly fix this is to pull the glass, weld in new metal, and reinstall the glass. Silicone is tempting but ultimately it's a bad idea for several reason. First, it rarely is successful since the silicone won't seal to the rust anyway. Second, the silicone gives off acetic (sp?) acid, which will attack the metal. Third, since the silicone doesn't adhere well to the rust, water is trapped under it and accelerates the rusting process. Finally, cleaning all the silicone off prior to a proper repair is a big PITA.