What was found
(CAN) DURING CLIMB, CREW SELECTED FLAPS '0' BUT NOTED THAT PANEL NR 4 DID NOT APPEAR TO RETRACT ALL THE WAY UP. FLIGHT CONTINUED TO DESTINATION AND FLAPS WERE CONFIRMED TO BE ALL UP EXCEPT NR 4 WHICH WAS HANGING DOWN BY APPROX 4 DEGREES. THE .5000 & .7500 PANEL PAIRS ARE PROTECTED BY A 3 TO 6 DEGREE SPLIT IN PAIR WHICH LOCKS SYSTEM, ONLY RESETTABLE ON GROUND. MAINT FOUND THAT FLEXIBLE DRIVE CABLE FOR NR 4 WAS BROKEN INSIDE OF EXTERNAL COVERING. A FACTORY INSTALLED CLAMP APPEARS TO HAVE BEEN OVERTIGHENED WHICH CAUSED A LOSS OF COVERING INTEGRITY ALLOWING MOISTURE TO ENTER CABLE SHEATH. LOW PORTION COLLECTED MOISTURE AND EVENTUALLY CORRODED ENOUGH TO ALLOW TORQUE TO BREAK STRANDS. MFG HAS BEEN NOTIFIED.