What was found
HNL FLT 125 EN ROUTE HNL TO PHX. DURING FLIGHT, THE RIGHT HYDRAULIC SYSTEM BECAME INOPERATIVE DUE TO LOST HYDRAULIC QUANTITY. THE FLIGHT DECLARED AN EMERGENCY AND RETURNED TO FIELD HNL. THE FLIGHT LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE FOUND THE AFT DIFFERENTIAL PRESSURE INDICATOR OF THE RIGHT ENGINE FILTER MODULE LEAKING. REPLACED TWO O-RINGS (LARGE O-RING WAS CUT). SERVICED THE RIGHT HYDRAULIC SYSTEM. RAN AND OPS CHECKED THE HYDRAULIC SYSTEM SEVERAL TIMES. OPS CHECKED NORMAL. NO LEAKS NOTED.