I've not seen any sort of hot glue epoxy used, but have seen them solder / aluminum weld them. you have to be very careful heating those areas with a torch. I once attempted to weld up some AC fittings on my own with some low head aluminum rods. it went well until it didn't LOL all was going good and then all of a sudden the whole area just went from a solid to a blob of melted aluminum on my vice!! oopsies!!
I hate that you'd have to remove the coating from the effected area, but I would try cleaning the radiator well with the garden hose and some dish soap, light brushing action not to damage any more of the fins. then after the wash and blow dry with the compressor, spray it off with some brake cleaner and blow if off again so you have it all clean dirt and grease free. get you some rubber bungs to seal off the hose nipples, have a squirt bottle of water and dish soap handy. use the pressure tester to fill with air and get it about 15 or so psi. then look and listen for leaks, bubbles from the soap. see if you can pin point exactly where the leak is.
idk if paint strip will remove the coating where the leak is to get bare clean aluminum to do the repair at or not.