Have it tig welded. I cracked the oil sender port on my block and no matter what kind of epoxy weld I tried no luck. I cleaned it real well and tigged it up and have not had a problem since.

Remove the tranny and then find someone really good at aluminum welding. Will be alot cheaper than paying for a new tranny case.

Tip: if you are going to have it welded, drill a small hole at each end of the crack to keep the crack from growing under the heat.