[Yosemite Sam]

That is something of a sticky wicket.

Fix it right... I understand anyones desire to have a dependable, good running no problems Cub, a tractor that you can climb onto at any given time, fire it up and do some work with.

In this situation, the only real job that that the rear cover does is to keep the fluid in and keep contaminants out. If you can successfully accomplish this, then I believe that it, for the most part, is fixed right. This is providing that the hitch will bolt on and be strong enough to it's job and the transmission has no mechanical problems.

If this tractor was mine, I would button it back up, using whatever means necessary to keep it from leaking (providing that you don't get a bunch of sealer on the inside of the case that could end up being sucked up into the pump) and use it as you normally would. In the mean time, I would keep an eye out for another (reasonably priced) rear end. Once acquired I would clean the new rear end, maybe paint it, and get it ready for installation. Should you find a period of time when the tractor is not in use, you could then remove and replace the damaged rear end at your leisure. Or keep the new rear end handy for a quick change just in case the original shows signs of problems.

The best I know is that the only other alternative you have is to try to find a replacement and change it out right now. These rear ends can be found, often times for a little of nothing, but that never seems to be the case when you need it right now...

Good luck with whatever you decide.