Thanks for the info.
The kit came today from Patriot Supply and it appears it's exactly what I needed. The wheel appears to be stainless steel and it comes with a new motor, mounting plates, and wire kit. It looks exactly like the old one but this one has the cooling fan in one piece
It also comes with extra mounting nylon lock nuts, new wire nuts and a tube of high temp RTV.
I installed it with no trouble and everything is back and running as expected. It's nice to be warm!
The more I think about it, the more I think there is some sort of design issue. Since all corrosion started right around the hub, I have a theory. From the last photo in my post above, it can be seen that there are really two mounting plates. The one is bell shaped and is attached to the actual motor. The second is a flat plate which separates the stainless steel wheel and the motor innards. There is a small slot at the bottom where air can be drawn up into the motor to cool it. My theory is that fly ash made it's way through the flat plate and onto the cooling fan. There is actually quite a bit of clearance around the shaft in the flat plate so this makes perfect sense.
In my opinion, there should be some sort of bushing or seal through which the motor shaft can ride which will help to keep dust and fly ash out of the actual motor internals. This would lessen the problem. Of course, it's probably easier to just make the cooling fan out of stainless steel... I can't think it would add that much cost.
Either way, for around $200 (after tax, shipping and including a bottle of super lube), I'm back up and running. I guess I can't complain too much. I do find it a bit odd since the old motor went out of warranty (according to the sticker on it) in April of this year!I truly hope I can't expect the new one to fail the summer after its warranty expires...