Re: Crack around top shaft tube
Put a pipe wrench on it, leaving the cutlass bearing inside so you don't crush the tube. See if the whole shaft tube has broken loose enough to move... If it has, you'll want to grind back to the existing tabbing inside and out.
If you can't move it... Grind down the existing tabbing on the outside to clean up the crack and build it back up from the tube.
Sometimes vibration shows poor prep, and other times it breaks things. Determine if you've got a case of things that shouldn't move, moving... If it was poor prep at the factory that vibrated it's bond loose, but you can't move the shaft tube, then you've got a surface repair.