How can my Pepper Mill shaft be either repaired or replaced?

My local hardware store put the top of the shaft of my European pepper mill into a re-tapping device - which they'd set to 2/32" - not realizing that the mill had actually been crafted to metric standards.
Consequently, they ended up reducing the diameter of the top of the 8" metal shaft; the crank which is meant to fit around and grab this top part of the mill shaft is no longer grabbing and turning it because of its slightly reduced circumference.
The rest of the shaft (the part which fits within the mill itself is intact).
This shaft diameter is not completely round but is instead, square on two of its sides.

Can this shaft be:
1. repaired?
2. or replaced?
3. or can the inner dimensions of the metal crank opening - (which slips over and is grabbed by the shaft )- be reduced so that the shaft fits properly within it once again?

This wooden pepper mill (appears to be rosewood and has a metal (pewter?) domed top. It was purchased in Italy MANY years ago and has no indication of manufacturer or actual country of origin.
The rest of the shaft (the part which fits within the mill itself is intact). This shaft diameter is not completely round but square on two of its sides.

Can this shaft be:
1. repaired?
2. or replaced?
3. or can the inner dimensions of the cranks opening - which slips over and is grabbed by the shaft - be reduced so that the shaft fits properly within it once again?