1974 Duster water leak

There could be a leak between the gasket and the body itself. I have seen cars look fine but once you start pulling stuff apart, rust damage is found. Hopefully this isn't the case here.
You can try injecting some sealant around the outside of the gasket but the trim will have to come off for access. The steel channel has to be cleaned out with a brush so any sealant you use will actually stick. This is not a 100% proper repair, just a Band-Aid sorts fix.