Coolant system Sealants

[Jonesy]

Exactly as Kurt said. Get the original repaired.

[Sauron327]

But that undermines the originality of the car. It doesn't make the car more original if the original parts are somewhere in a box.
And you then get to store the second radiator.
Just get the rad repaired.....

Perfect answer. A person will restore a part, buy a replacement and put the original on the shelf. This seems to be the trend these days. Most are checkbook car owners with zero mechanical or bodywork skills.
Real gearheads are rare today. Lost track of how many radiators and heater cores I've had rebuilt. I have sb and  bb tanks in stock.