It might not have to be replaced. Radiator shops PROPERLY fix radiators every day, and for a lot less money than replacing. All those stop leak products are good for is emergency get-you-off-the-road-and-to-the-closest-shop times. I have seen some of those do more damage to an older motor, then you’re REALLY going to be spending some money. Do it right.
P.S. Always change the thermostat when you open up your cooling system.
transman