It would be best if you could post a picture of the location of the crack. That being said, JB weld may, and possibly will work. The rear axle housing undergoes normal "squirm" and flexing by just being driven and used normaly. So does you engine block. Stress is induced by the engine hp and torque applied to the internal componets of the rear axle, which in turn transmits that twisting motion to the outer housing while the power is being applied to the ground as you get along on your tasks.
I would seriously consider welding the housing if the crack has not spread apart the casting. I would also get a good, or even certified welder who is familar with welding with Ni-rod. This is a special high content nickel welding rod specifically for welding cast iron.
If your housing is aluminum, again I would find someone who could TIG weld the crack. Of course the fluid has to be drained, and if the welder is familiar with the technique of burning the oil off while he lays done the repair bead.
Reinforcing the area is also another good idea which has been mentioned.
Even if you have to drain all fluids, flip tractor upside down, it is still better than a complete tear down, parts, labor expense. For what could be another under designed new part, which my fail in the future.
It would be most interesting to see pictures, and try and tell if it is a design flaw, or materials failure. Cast parts do have inclusions cast into them by accident. And every now and then one gets by inspection.
Let us know if we can help you futher. And if you can post some pictures.
