What was found
ON FLIGHT 3385 - CREW REPORTED DURING CLIMB HYDRAULIC SYSTEM 1 QUANTITY WAS IN NORMAL RANGE PRIOR TO DEPARTURE. 15-20 MINUTES INTO FLIGHT SYS 1 BEGAN TO DECREASE FAIRLY RAPIDLY. CREW REPORTED THEY COULD WATCH DECREASE OCCUR. QUANTITY INCREASED SLIGHTLY ON GEAR EXTENSION. QUANTITY NEVER REACHED AMBER RANGE BUT CAME CLOSE WAS DECREASING AT SUCH A RATE THAT SUFFICIENT QUANTITY AT STATION OBB WAS QUESTIONABLE. AIRCRAFT REMOVED FROM SERVICE. REPAIRED LINE IN HYDRAULIC SYSTEM NR 1 UNDER FLOOR AT SEAT 8 IAW JIC 20-10-03-300-801A. OPERATIONAL AND LEAK CHECK GOOD. AIRCRAFT RETURNED TO SERVICE.