Rainwater Leak into 1978 Shortbed Cab

[gmbellew]

I know this is an old thread, but wondering if anybody had an update. I have recently experienced the same thing. I suspect it is the windshield gasket along the top of the cap corner on the driver side, and it is running down the A pillar and into the cab along the top of the dash.

I plan to soak water into the cowl area to rule that seam along the firewall out. if that doesn't produce water, I plan to seal along the top of the windshield and then soak that area after a 48hr cure to see if I have resolved the issue.