Larry, The gasket that fits over the top of the pinch weld is split. Once the gasket is placed onto the pinch weld, part of the gasket is on both sides of the pinch weld. (like its on both sides of the glass). Often glass companies will only put sealer on the outer side of the pinch weld (if they put any sealer on it at all) but don't put anything on the inside of the steel. The problem with that is, any gap in the seal to the metal on the outside, or any defect in the metal, or any defect in the seal itself will allow water to well up and seep between the inside of the pinch weld's steel and the rubber gasket. That water build up eventually runs out between the rubber on the inside and the metal under the rubber gasket. You usually see the effects of this on the bottom corners of the windows, but the water intrusion can come from any place around the metal.

The typical cause of the water leak between the gasket and the interior metal is often places where the rubber gasket doesn't lay perfectly flat against the outer body at the corners.

The rear window on my coupe has a pretty tight corner at the top edges. The corner is so sharp, the the rubber puckers away from the car body on those two top corners. Those two areas have been bonded down a couple times by the glass guy with urethane and now lay pretty flat. The problem is, in heavy rain, water still pools at those two corners, and ends up running out between the rubber gasket and the inner steel at the bottom two corners. The last time, I made the guy put sealer on the inside of the gasket, all the way around. The water leak has stopped, even though I can still see water that pools at those two top corners.

Seal both sides of the glass at the pinch welds. It may make it harder if the glass ever has to be replaced again, but the current glass is now sealed. Gene