Are you the original tractor owner?  Ever use the "goo" bar's leak to plug a leak? May need rodding out.

One thing nobody has mentioned,, Check the water pump bearing. Loosen the Alternator belt, shake the "pee" out of the fan, does it wiggle around? if so, you'll need to pull the water pump and have it rebuilt.  Your local JD shop or whoever you choose can do it, or you can do it yourself if you have a good press for the bearings.  The fins on the pump may be gone, so everthing looks ok outside but the fins inside could be shot too.

Don't put off rebuilding the waterpump if it's loose at all.  Under full load the fan is really spinning,, and if the bearings go out completely,, the fan will do a real "Number" on the radiator. Likely eat the radiator and ruin the fan!

Dad found that out years ago when he was alive, he always waited till something was "really broke" before  fixing,, he knew the waterpump bearings were going out but ran the tractor anyway...  A simple waterpump rebuild turned into a Brand new radiator and fan PLUS having the waterpump being completely replaced instead of just getting new bearings put in...

New Radiator from J.D. for a 4430 is way north of $800 if your feeling flush.

Just got through replacing the radiator in a 4430,, it was so bad on the inside rodding out the deposits was the only thing keeping if from leaking...