C-bodies don't use wiper seals, the pivots are mounted externally to the cowl sealing. That's an A-body problem, I believe.
As mentioned, check the kickpanel vents - more specifically, the drainage out of them at the base, behind the fender's trailing section. If those drains block, water can rise enough to overflow the vent and get into the car.
If the car has had enough debris get into the cowl grille at the base of the windshield, and accumulates and stays moist, it can rust the cowl out over the years. Those typically rust out thru the firewall, but I have seen one rust a pinky-length hole thru the rearward panel, which is the interior shell right behind the dashboard. It poured a significant portion of water in when the car was washed. Unfortunately the way those cowl panels are welded together (the metal's shape, that is) it causes troughs and seams where debris can sit. I would encourage all of us to keep that cowl rinsed out periodically if the car sits under any trees.
And of course the AC drain tube and windshield leaks should be evaluated too..