Some of these hooks were nothing more than a steel rod wedged in a hole while others were a gouged out portion of the arbor. If yours is a steel rod, punch out the remnant and replace it.

If it is the gouged out type, your arbor hook can be replaced by drilling a hole through the arbor, tapping it, then making a screw to fit. I make the screw so it has a shoulder and a large head that can be shaped to look like the original hook. The threaded body should protrude beyond the arbor enough that you can peen it over and secure the screw. File off the head of the screw so it looks like the original hook and file off the peen so it is flush with the arbor.