What was found
PHX - EMERGENCY - FLT 0005 - YELLOW HYDRAULIC SYSTEM INDICATED LOW PRESSURE AND QUANTITY, MADE NORMAL LANDING, BUT BRAKES OVERHEATED. INSPECTION OF HOT BRAKES. AFTER BRAKES INSPECTED TAXIED TO GATE, HYDRAULIC QUANTITY WHEN AIRCRAFT TAXIED IN WAS "0". BELLY OF AIRCRAFT SOAKED WITH FLUID FROM W/W BACK. MAINTENANCE FOUND QUICK DISCONNECT FITTING LEAKING AT POWER TRANSFER UNIT. REPLACED O-RING IN QUICK DISCONNECT FITTING, SERVICED YELLOW HYDRAULIC SYSTEM TO FULL AND PRESSURIZED SYSTEM, NO LEAKS NOTED.