I've seen similar on bikes that weren't greased well at the bucking bar - considered pressing a brass bushing in there, but with several dead motors around here, it was easier to just shove in a used shaft.
This happened to me last year. I made a new bar from a wider drill-bit and greased the heck outta it. It extended the part's life by about 2-months. I like crassius's idea though...sounds viable.
I would have used some old valve guides that I have lying around, it *should* work well, but it is much too much work for a shaft that is so easily replaced.