Water leak inside 65 barracuda

Why not just get under the dash with a flashlight and have a look see? If the "Top Hat" vents are leaking you will be able to see the rust and water if its the Windshield seal "like mine that leaks" you will have to take it out. and seal it again.

Another thing to do is get under the dash board in the garage with the lights out and put a droplight on the cowl, you might see light holes....