What was found
(CAN) REFUELLING WAS C/O, MASTER REFUEL PANEL CHECK C/O TO CHECK VALVE FOR OPERATION, WHAT WAS NOTICED, FUEL CAME OUT OUT OF THE LT NACA SCOOP APPROXIMATE 2 GALLON, THEN STOP. MAINT WAS ADVISED,THIS WAS ONLY HAPPENING WHEN A/C WAS PARK OVERNIGHT. SO MAINT CREW FIGURED THAT THERE WAS A BAD O-RING IN VENT SYS. A/C RETURED TO MAINT, FUEL WAS DRAINED AND FUEL PANELS REMOVED, FOUND VENT LINE, FUEL WAS LEAKING THRU IT. PIPE WAS REMOVED, FOUND PIPE HAD A HOLE THRU IT, CORRODED. PIPE HAD AN A CAP INTALLED TO THIS VENT LINE, A UNAPPROVED MOD WAS C/O ON VENT SYS. BY DOING THIS UNAPPROVED MOD WATER COLLECTED AT BOTTOM OF PIPE AND CORRODED THRU. S/B WAS COMPLIED WITH AND SYSTEM CHECK SERVICABLE. (TC NR 20060515003)