Ya I had that problem at first, thru continuous testing I found that if you make the shaft and agitator of thick gauge steel it will last longer. The shaft and bearing was 1in d the bar is over a 1/4in thick.
I am aware of the corrosive products be they are easy to see. Also I have sort off a zinc it wares out fast to protect the other metals, I think I refer to it as a catalyst in the patent. when you can burn as hot as you can reduces the nitric emissions, the hotter the better, I try to achieve a blue flame. There are quite a bit of protective coatings that are used.
Did you know the burning corn is totally unregulated by the EPA.
Of another concern is the use of a superheater, these can glow red. My preferred material is 316L SS.