It's pretty common for these transmissions to break the cup that guides the shifter. The repair is to weld the cup back on. It looks like yours was sort of welded.
Go to the tech library:
http://onlycubcadets.net/forum/forumdisplay.php?f=19
and look for the three threads in a row about shifter repair.
You should find what you are looking for.
I think I saw one vendor who had just the cup, which you could probably use to fix yours, if you know someone who can weld better than the previous chap who worked on your machine.
Good Luck!