Duster windshield removal/replacement
I fought this for many years on many a-body mopars until I figured it out. We have a Barracuda here right now with the same problem we have to correct. It leaks at the same place on both sides , Fuse box and top of glove box.
Some cars leak right from new and some don't. Reason why most all of these cars have rusted out floors. Its not the wiper pivots and its not the windshield gasket. When ever you pull the windshield on these cars there is a channel that gets exposed that needs to be resealed before reinstalling the gasket. Usually when removing the gasket it pulls the sealer from the side of the channel. All a-bodies 67-76 have this channel and most all leak. And No wiper seals won't fix it.
I have some bare body shells here I can get pictures of when the snow stops. They are in Trailers that I won't open to moisture.
Explaining it won't help without pictures. But there are drain holes that lead into the cowl from the lower windshield channel for a drain. These drains are open at both ends when one end should be sealed with seam sealer. If not they will empty into the car. Sealing the drain opening will only cause the chanel and trim clips to rust. You must seal the end of the channel that leads to the interior.
I just remembered there is a body in the garage next door. I'll get pictures of when I go retrieve my golf cart with the skid loader. I got it stuck coming home last night in the snow. Wait for the Pictures.