I know that i have a pass foot well leak. I removed the carpet to allow it to dry out. I check the AC drains. We have had rain for the past day. I tried looking for the source of water. The insulation/sound deading material on the firewall (behind the blower motor) is soaked.

I know possible causes is the windshield (mine is original), roof/a-pillar joint (mine had some hair line cracks that i put RTV over), sunroof drains.

What is my most likely cause? and any tips for determining which one.