I run into this type of situation every now and then while working on machinery. You need to get yourself some pointed 90-degree picks, no larger than 1/8" diameter. Work one pointed pick under one end of the broken ring while holding the ring still in the groove with the other pick. Gently work one end out of the groove, continuing around until you can get a grip on it with some pliers. Be careful not to stab yourself! Regards,