Since using -= does not work on object refs, the combat hook and mainhit scripts in the distro need to be modified:
combatHook.src
line 262
was: shield.hp -= 1;
should be: shield.hp := shield.hp - 1;
line 313
was: armor_hit.hp -= 1;
should be: armor_hit.hp := armor_hit.hp - 1;
There appears to be no weapon wear in the hook.
mainHitScript.src
line 118
was: armor.hp -= 1;
should be: armor.hp := armor.hp - 1;
line 241
was: shield.hp -= 1;
should be: shield.hp := shield.hp - 1;