This worked for me. I upgraded to cIOSX Rev21 and installed Priiloader.
Unfortunately my preowned disk was scratched. I had to go back to the shop and get a replacement disk before it worked. Now my autistic son can play without me worrying about him scratching the disk.
@TheBandicootAddict: Please can you include a link to a useful Priiloader tutorial (unfortunately this one does not include the latest hacks_hash.ini instructions)? It is not obvious to casual wiihacks Googlers that Priiload is needed.