Repair of a leaking MGB heater duct
Leaves had clogged the drain hose beneath the outside vent in the area forward of the windscreen. Rust had claimed the floor of this vent and it leaked .... badly.
With the heater box out for restoration I vainly sought some way to patch the holes, but they were invisible, and all but untouchable.
My solution was to cut three sides of a rectangle in the firewall (squared U shape), behind the heater box and above the shelf. Peel it open like a tin can and the rusted floor of the duct will be accessible. I used POR-15 and some fabric to cast a new floor, then closed the door with a couple of tack welds and a bead of silicon.
The incision is invisible behind the heater box, and water no longer floods my foot-wells.