There is a product sold (I bought it at a circle track supply outlet)
it is a plastic cord 3/16" diameter. The radiator tubes are carefully heated with a low temp torch and then you touch the plastic to the tubes and melt it much like solder, it does not flow out like solder but is applied in small "clumps". When heated the plastic is very stringy and has a lot of body. Be careful with the heat, too much heat and the fins will "Disappear!"
In lieu of total replacement this type of fix OR some sort of radiator stop leak is your only alternative.
Another option might be a glue gun & glue sticks commonly used in crafts.
Just be sure the surface is clean, free of
oil, coolant etc.
Applied properly this worked well.
Rick