Small hairline crack around the output shaft
 

I have a 99 GMC Sierra 1500 5.3 4x4 with the 4l60e. I dropped the transmission to replace the bellhousing and noticed a small crack near the output shaft. Anyone ever have something similar happen. On a side note everything started happening after replacing the transfer case adapter that cracked. I believe all was due to a bad transmission mount. Think some JB weld would work or another transmission.
https://cimg8.ibsrv.net/gimg/chevrol...08a697473e.jpg

JB Weld MIGHT work, but it could throw the balance off. It would also need to get into a crack like this. Perhaps heat could be applied so that it did penetrate into it, not I honestly think this crack will still expand.no matter what. JB Weld is unlikely to work for this condition.

You really need to be able to access the inside of the case to be able to properly assess and/or repair that; however that’ll require transmission disassembly to access it. And if you’re gonna go that far, why not rebuild while you’re at it?

IF there’s no other damage, JB weld would probably work but it would require sanding/reshaping once finished. There’s a bushing on the other side that needs to fit into the case for proper alignment.

IMO, you’re just as well off getting a good transmission from a salvage yard, unless the idea of tearing it apart is appealing to you.