What was found
EN ROUTE FROM PHX TO PDX APPROXIMATELY 2 HOURS INTO FLIGHT RECEIVED A GREEN HYDRAULIC SYSTEM RESERVOIR LOW LEVEL ECAM MESSAGE, FOLLOWED BY A NR 1 ENGINE GREEN SYSTEM HYDRAULIC PUMP LOW PRESSURE. FOLLOWED ECAM PROCEDURES AND SHUTDOWN THE POWER TRANSFER UNIT AND GREEN HYDRAULIC SYSTEM PUMP UNTIL ON FINAL APPROACH. DECLARED EMERGENCY, GREEN HYDRAULICS SYSTEM WORKED FINE ON LANDING. MAINTENANCE FOUND THE LEAK MEASUREMENT SELECTOR VALVE LEAKING. REMOVED AND REPLACED LEAK MEASUREMENT SELECTOR VALVE. OPERATIONAL AND LEAK CHECK GOOD IAW AMM 29-19-41-401.