I would guess that this is a Peck heater? If so i am told by a local (Mog) dealer they are no longer available, neither is the rubber gasket that inevitably perishes, i made a gasket out of, (guess what), neoprene……
Self adhesive neoprene tape around ½" thick, build it up to fit the underside of the bonnet, it requires a slit to fit the top rim of the heater intake, then trimming to make the correct angle of slope.
Not sure what i will do if the heater packs up but i am sure the replacement make will fit ( anybody know what make and model that is?)
These heaters are pretty simple things so not sure the newer ones are any better?