Neglect is the most common cause of radiator failure in classic cars. Most enthusiasts do not perform regular maintenance for the cooling system, such as flushing the engine block and changing the coolant, which should be done on a 2-year schedule.
In my experience fan belts, hoses, clamps and water pumps should also be checked periodically and replaced as necessary. Never use STOP leak, it will completely swell and clog everything including your engine, radiator and heater core.
Maintenance will undoubtedly prevent a lot of future problems, such as clogged radiator leaks, blown head gaskets or ruining the entire engine.
Care and prevention are well worth it and better than being on the roadside waiting for a tow truck.
About 20 years ago a gentleman called and asked us to construct a special radiator for a 1910 Oldsmobile to be entered in the Great American Race, which is held yearly in the US from coast to coast. He insisted that he had to travel through the desert and needed optimal cooling. We completely disassembled the radiator, cut a facing off his original core for authenticity and
added a modern heavy duty copper-brass core with facing on the front side for originality. On a later date, he called and thanked me for our work. He traveled through the desert of 112 degrees without a hitch. Proof that a radiator design and maintenance is key.