What was found
(CAN)DURING THE ROUTINE INSPECTION AND TEST OF THE OXYGEN SYSTEM A HISSING NOISE WAS DETECTED EMANATING FROM BEHIND THE LEFT SIDE PANEL OF THE CABIN. UPON FURTHER INVESTIGATION THE UNION FITTING IN THE OXY GEN LINE AT FUSELAGE STA. 176.5 BETWEEN LINE P/N 50560009-63 AND P/N 50560009-75 AND EACH "B" NUT ATTACHED TO THE LINES WERE FOUND TO BE CORRODED TO THE POINT OF DISINTEGRATION.