I have heard a few different ways to fix a pin hole leak in a radiator. I have heard put a small amount of black pepper in the radiator, or use jb weld to patch the hole, and not to use the stop leak antifreeze.
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Many years ago, I brazed my non-aluminum, non-plastic radiator pin hole shut with a metal coat hanger and disposable propane hand torch. Never had a problem again with that radiator and it lasted for many years.
Otherwise, scrubbing with acetone and using JB Weld "Extreme Heat" and a piece of metal flashing might be worth a try (follow safety procedures).