Hi RLP,
Seems a strange way of doing things, was it working ok before you removed it seeing it was rusted solid as you would expect it to be. If it was wprking ok, I would be inclined to drill and tap the disc about half way along the keyway slot and fit a grub screw in it to hold the key and the disc solid, and then work out if it needed adjustment to take up for wear which I would imagine would be minimal
