What was found
AIRCRAFT WAS GROUNDED: PILOT REPORTS HYD "G'" RSVR LO LEVEL "G" ECAM. PUMP TURNED OFF WITHIN 5 MINUTES OF ECAM, PUMP RAN APPROX 10 MIN LATER FOR GEAR EXT UNTIL LO LVL MSG REAPPEARED. EMERGENCY WAS DECLARED. MAINTENANCE REMOVED AND REPLACED #1 HYD PUMP DELIVERY LINE CHECK VALVE O-RING , NO LEAKS NOTED ON GROUND IDLE RUN, ALL WORK IAW AMM 29-11-36-400-001 AND AMM 29-00-00-280-006. ENG PUMP RAN LESS THAN 10 MINUTES WITH PUMP SWITCH OFF AND FIRE VALVE OPEN, NO FURTHER DISCREPANCIES NOTED.