You will now want to score the shaft using a utility knife, or other sharp object. The tip of a sharp screw driver can work. Or you can rough it up with thick sandpaper. In any case, the idea is to create a surface that is rough enough to restore friction between the shaft and the grey gear.

It isn't easy to take a picture of, but the shaft has been scored in a cross-hatch pattern.

You can now re-insert the shaft, chasing the drill bit back out, ensuring that the numbers remain in sync. Once the shaft is all the way back in, you can then use a small punch and a hammer to tap the brass retaining ring back on the end of the shaft. If needed, support the brass gear with a small piece of hard wood.