Fresh air intake plenum leaks

The fresh air intake ducts on my ragtop (on all '64 Darts, according to the manual) are fed by a "ram air feature" from what I believe is correctly called a "plenum" at the base of the windshield. The ducts attach to the floor of the plenum at locations that are rolled upward which, it seems, are designed to prevent water in the plenum from entering the ducts. There are drains at the sides of the plenum, which can be seen and felt with some difficulty under the hood torsion bar ends. Pouring water into the plenum through the grill at the base of the windshield results in water draining properly into the inside of the fender and on out the bottom.

My problem is that water is leaking from the plenum, not into the fresh air ducts, but down both sides of the firewall. It seems the floor of the plenum is leaking at the area that is rolled up. I have found no serious rust issues on the car, so I don't think there are rust holes at the lip of the duct holes in the plenum floor. I've removed the driver side duct, and stuck my hand up through the passenger side duct and can just barely feel around the lip, but don't feel any holes. I've cleaned the accumulated leaves from the area with a long extension on a blow gun powered by my air compressor, inserted through the grill at the base of the windshield, up the fresh air ducts, and into the plenum by way of the oval holes in the firewall, and the area seems to be free of debris, but there is just no way short of making new holes to get an eyeball look at the areas.

I'm at a loss to figure out how to apply some kind of sealant aroung the rolled up lips in the plenum floor. Any ideas?

I stripped out three layers of old carpet to find the mildew in the jute padding under what I suppose was the original carpet. I've primed the bare floorboards, installed new foil and foam type insulation and bought new carpet and I'd like to fix these leaks. HELP!!!