I'm running a 21I-TA Cobra 42 lathe and the turret will index normally for all tool pockets except tool 12. Tool 12 will index in the clockwise direction (from 11 to 12) but not in the counter clockwise direction. We had this problem in the past and it was due to a broken retaining ring. However at this time we don't have the option to take the machine out of operation to inspect for a repeat of the previous problem. Rather than programming unnecessary tool changes, is there a way to limit the indexing to only one direction? Thank you for your assistance.