If it was mine since it isn't any good this way I would clean the crack and sand a little around it. Then use JB Weld to put a gob over it and put a patch of same kind of material on top of it. You could cut some black plastic off a old car part if you need to. It will work and last many years if you also band aid with the plastic for more holding strength. People have fixed manifold leaks with the stuff in the past. I have used it on a fuel tank still holding. Besides JB Weld is way cheaper then a new JD Radiator.
I would try a radiator repair shop if you have one in town. It seems to be a lost art form but in the past, you could have the end tanks replaced.
Buy a plastic welding kit. They start at around $60 and work just fine.
JD 48" blade, JD 30 tiller, JD tractor mounted electric spreader, JD hydraulic sleeve hitch. 48" deck
48" York rake, 56" box blade, mid row buster, dethatcher, aerator, 900lb roller
Various Heavy Hitch adapters, ball hitch, hook, 2" sleeve hitch, etc..
3200lb. hitch mounted winch
Rear electrical junction box with external rear LED lighting
Polar 1700 3/4 ton cart with side rails
Power King 5" towable chipper
And a smile every time I sit in the seat.