1974 Duster water leak

If I recall correctly there are several little windshield support tangs formed along the lower window opening. These are punched out from the inside, and leave similarly shaped sloted holes where they came from. These holes are usually covered by the windshield gasket. But no sealer is used at the factory. As the gasket ages it shrinks. Perhaps your gasket has pulled up and exposed these slots.
The only way to prove this is to pull the trim off. I seem to remember 4 or 5 of these slots on my 68 Barracuda. They should be covered by the lower edge of the rubber gasket;should be.

I should say that this memory is a little cloudy in my brain, and I'm not sure that it is 100% correct.