Yes, the cast-iron radiators are cast hollow, so the feet can be punched through to leak. Although they are metal, they are more delicate than they appear and are not as rugged as a car block. That is why the words 'carefully' are used to lift the radiator from exposed parts using a block of wood as the base to protect the floor. Wooden door jamb wedges should be slipped under the slightly raised feet.
Your 'I used a hammer to wedge the crowbar under the radiator feet.' shows that the radiator feet had sunken into the wood floor and your crowbar hit the side of the feet, making a hole. There may also be some floor damage. I will place some pictures of how to lift a radiator without force on my web site. Plumbers are careful not to damage the floor, as their customers would do more than complain.
There is a product named 'Black and White', a sulphur compound, that when properly and carefully heated will seal the hole. This requires removing the radiator and turning it about to make the repair after thorough wire-brush cleaning and maybe some chamfer filing. This is easier than brazing the holes shut.
I have heard an old story where the homeowner wanted to make the radiator a little shorter, so cut the legs off to fit the radiator under the window. This had a much more permanent effect than your cracking the foot.
Perhaps there is some other misunderstanding. Raising a radiator does not stop leaks, it stops banging by sloping the radiator toward the steam pipe. By moving the water out of the radiator, there is less water to splash up into the vent. The admonition is to move the radiator as little as possible as it may cause leaks through loosening the attached pipes, not stop them.