What was found
(CAN) AN OIL LEAK WAS DISCOVERED BY MAINT IN THE OB SIDE OF NACELLE. AFTER CLEANING AREA, OIL WAS OBSERVED RUNNING DOWN OIL RETURN LINE (COOLER TO TANK)FROM AN AREA WHERE A WIRE BUNDLE WAS LAYING AGAINST LINE. A WIRE HAD BEEN CHAFED THROUGH AND BARE WIRE WAS ARCING AGAINST OIL TUBE CAUSING A PIN HOLE IN TUBE. WIRE WAS POWER WIRE FOR THE HYD FIREWALL SHUT OFF VALVE. ARCING ALSO DAMAGED WIRE FOR OIL SHUT OFF VALVE. REMAINING AC IN FLEET WERE INSPECTED, ONE ADDITIONAL AIRCRAFT HAD WIRE BUNDLE UP AGAINST THE OIL RETURN TUBE. DEFECT WAS RECTIFIED. DAMAGED TUBE WILL BE REPLACED WITH A SERVICEABLE UNIT AND AC WILL BE RETURNED TO SERVICE.