Radiator leak

[Maj]

Which knead it ? there is a radiator and fuel tank repair that will work on the wet surface , others will need it sanded back and chemicaly clean to stick,

another option would be to ask a refrigerator repair shop if they can aluminium braise with low temp alloys, often used in there trade , sort of stuff you can weld coke cans with and sometimes sold at swap meets ..
or plan c would be to rinse and dry the internals open the hole enough to squeeze in some silicone then pinch the hole closed and wait 24 hrs before use