Hi kermie,
Thanks for sharing the detail of the situation, it really helps paint the picture. For the sick leave, if you pay a full week but the employee only has 28.631 hours available, MYOB will show negative sick leave hours, and that’s normal. It just means the employee now effectively owes you those extra hours. If you don’t want the balance to go negative, only put 28.631 hours against sick leave. For the holiday pay being wrong for a long time, the cleanest fix is to work out what the correct current leave balance should be. After that, do a void pay to bring the hours to that correct figure and let it accrue normally from there. You can also check out this link about adjusting leave entitlements for more info and examples on how it all works.
Cheers,
Doreen