Gas and Oil Home Heating Furnaces - Repairing cracks on hot water radiators

I have a cast iron hot water radiator that has a hairline crack around bleeder valve. I was replacing the old style knob type valves on my radiators (since my children like to play with them, not good idea since the water is at 180 F degrees when the radiators are in operation) with screw type valves. On the last radiator where I tried to unscrew the valve, I caused a hairline crack around near the bleeder valve socket. I managed to remove the remains of the old valve and the threading on the radiator is OK.

I was told welding cast iron is not a good idea as option to seal the hairline crack. Is there a way to seal the crack with something like epoxy ?

I would prefer to fix this old style radiator as opposed to replacing it with a "modern" conventor type radiator.

Thanks "Z" man