Don't listen to these naysayers.  

How much of the shaft is sticking out beyond the seal?

My bike has two inches sticking out.  That is a lot of gluing surface.  Done right it will be waterproof, heat resistant, and last a lifetime.  Here in CA we know how to glue a single bolt into the concrete ceiling of a parking structure and hang a truck on it.

That shaft is toasted. The cases must be split to replace the shifter shaft. You've nothing to lose by welding it on. I've done it on two XRs, here's how.
Lay the bike on the right side with the shaft pointing up. Place wet rags around the shaft and on the surrounding area to keep welding spatter off everything. Place a trickling garden hose at a strategic position so that the water flows over the area around the shift shaft, this will keep the seal area cooled off. Weld the shifter on, you're ready to go riding. Use an OEM shifter, they are very malleable and will bend instead of breaking in case of a crash, and will not further damage the shifter shaft.

Thank you for the help on this. My buddy welded it on yesterday and it seems to be working a charm. I have my fingers crossed that no other stupid failure is coming up next.