I would think that if that was a press fit, everytime the stove and grates got good and hot, the expansion of the hole would allow the shaft to spin in the hole in the lever.. If it was CUT, then I'd maybe believe it is supposed to have an 'expansion crack' but I'd say the part is broken, I certainly could be wrong, but Harman builds a pretty tough heavy duty stove, and a press fit in this location doesn't make a lot of sense to me..
Maybe press it on, then put a spot of arc-weld on it to keep it in place, If it was intended to have an expansion gap, then it should have a pinch bolt to close the gap and clamp the ring tightly onto the shaft..
I'd say it is a broken part.. untill proven wrong...
If it was mine, I'd push it back on, make sure the handle was where I wanted it, then tack-weld it in place, where I could get a 4" grinder in to grind the weld off if needed.