I had my IH 424 radiator fixed at a radiator shop for about $100 this summer. I've done a couple small radiator fixes before like a loose hose connector, but the 424/444 radiator has 3 or 4 rows of tubes that are stagger and they would be a nightmare to fix if you got core to hot trying to fix the seam. Radiator repair require quick heat to only heat the area being worked on or the heat spreads and unsolders other joints.
Update on the radiator, There ended being about 5 leaks, every time I would get one fix and pressure test there would be a new leak some where else. The core is also leaking in several spots which is only now showing up after fixing the big leaks, the big leaks made it impossible to find the small ones. I called a radiator shop recommended by a tractor parts store and they said it will cost over $450 to re-core and fix my old radiator. They do not make a new one for the 444 so I decided to order a new radiator for the model 140 that is the same size and has the inlets and outlets in the same place. I will probably have to fab up the mounting brackets to make it fit but, I would rather do that then take a chance spending the same amount of money on repairing and old radiator.
You would likely be better off using your brass tank top and bottom and having the radiator shop put in a new core. The new radiator is likely plastic top and bottom just like all the cars and trucks now. Check the construction on the "new" radiator before plunging in and getting a crappy new radiator when for the same money or less you can get a good solid brass one. It will be just like new when finished because all the use is the top and bottom of your radiator. I had this done when my JD 332 garden tractor radiator started leaking. It was about $200 less than a new one from JD and I have a solid metal one not plastic.
If its to the point of leaking, you can just about bet that its due for a good cleaning too. Best off just taking it to a good rad shop and having it rodded or boiled out and then have them re seal it then fully pressure tested, then you wont have to worry about the thing coming apart on you for a good long time