The firewall, where the heater unit was. The heater unit was standing on the rusty patch. At the centre of the bottom edge of the picture was the gearbox. The opening near the top centre is under the ventilation flap in front of the windscreen. The rust was cause by rain water entering via that flap and trickling down through the heater unit. The bottom of the heater unit will be equally rusty as this body area. The openings left and right (just under the blue body part) feed hot air from the heater unit to the two demisting slits above the dashboard.