Ida thought that pinging out the key with a small chisel, lapping with coarse then fine grinding paste till it fits, then re-fit the key and prop with perhaps some Loctite Shaftloc or something similar would do the trick.

It should also be done up to the correct torque - which I think is usually F*****g tight.

I had the case of the shaft anode loosening - but I think that was because it was a cheap crappy anode without the steel insert to hold it in place properly.