Introduction;
When I bought my ’74 it came with a brand new Alpine stereo with speakers in the doors. It also had a new windshield seal and lock strip, but an old, pitted, scratched glass. The space between the body and seal was completely filled with urethane sealer.
Conclusion;
P.O. bought a new sound system from someone who did not know what the vapor barrier was for. It wasn’t just loose, but missing. When the rains came, the floors flooded, and someone decided it must be the windshield. He could not afford the windshield so he had just the seal replaced. That didn’t work, so he had the goop squirted in. That didn’t work so he sold the car.
Epilog;
I bought from a used car lot, never met the P.O, but if you listen closely, the car can tell you stories. Always keep your vapor barriers water tight.