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Like Barnett mentioned, first determine where the leak is coming from. Clean up that mess, run the motor, drive the car a few miles and double check. I'd also check the trans fluid just to be certain coolant is not getting into the trans fluid from a leaking trans cooler inside the radiator. These work good for stopping minor coolant leaks and do not clog cooling systems. They will make the coolant look a little muddy in color.

I would clean all around the fitting with a brass or steel wire brush and determine exactly what is leaking first.

Technically my dad did for him. And it was well before my adventures into Mustangs. Both his cars were impeccable restorations that would win awards everywhere he went. So much so he stopped bringing them to shows. He ended up with parkinsons and as time went on, turned into dementia. The last straw was him "working" on the car fixing an issue that he had back on the car many moons back. My grandmother told my dad to sell them and unfortunately for my dad, who grew up restoring the 34, didnt have the time, or drive to keep it around due to him having to take care of gramps. Sad story all the way around but its life.