water leaking inside thru cowl grate
Check wiper pivot seals too
When I had windshield-area leaks in my Dart it was pretty much everything BUT the wiper pivot seals (though I replaced 'em anyway). Mine's a '67 post, and the 68-up windshield gaskets seem to fit a little loose, which was 90% of my problem.
Lots of good advice here, be careful cleaning out the cowl vents...sharp edges alert!! I wrapped some duct tape around my wrist so I didn't slice a vein.
Also, don't overlook random holes either in or near the cowling (mine was leaking around the screw that held the F tee for the windshield washers), also look for holes behind the kick panels (had one of them too).