Finally Found My Phantom Water Leak...help.

So I have been chasing down a water leak in my car for a while now. I've only ever noticed it leaking in very heavy rain or when I have driven it in rain. I have tried taking my garden hose before and spraying it in various places and finding nothing. So I stopped driving it in the rain, cleaned out my sunroof drains with compressed air and it seemed to no longer leak, so I painted my floors with POR 15 as a preventative measure and I never thought much more of it. We had a very very hard long rain here a few days ago and when I came home from work, I put my windows down and noticed a strange looking streak on the floor and sure enough it was water soaked up through the carpet on the passenger side. So I ripped out the seat, soaked it up and began investigating. After spaying lots of water, I finally noticed it beginning to leak in. I sprayed in between a little crevice between the passenger fender, cowl, and underneath the weather stripping for the windshield and it started coming out of this hole in the floor. Where could this be coming from? I had a new windshield installed a few years ago. And it had leaked before that.

Thanks!

Thanks. I really can't trace this leak. The tiny rectangular hole that meets the floor pan is a piece of metal that is spot welded to the floor seam/firewall. So I have no idea where it could be possibly be coming in at. Have you checked the seam of your floor pan behind the drivers seat? Sometimes that adhesive used to seal it will crack.

Those pictures are directly below the dash on the passenger side where the floor board meets the firewall.

Good call. I will pull the weather stripping and clean all around and POR all around. There are these "tabs" that hold the weather stripping into place, so I thought about putting a dab of silicone on these (not enough to make them impossible to get out again) and see if it helps seal things up. I have it parked in the garage and will leave it there for a few days to ensure everything dries out because I don't want to seal moisture in and do any more damage. It seems that this is a common problem on Mustangs for various reasons, so I will post updates for future reference. Thanks again!