What was found
MAIN FUEL LINE, PN 95153-27 (LEFT) AND DASH 28 (RIGHT) CHAFED 90 PERCENT THROUGH BY CABIN HEAT DUCT, PN 63633-91, IN AFT NACELLE. INSPECTION OF THIS AREA REQUIRES REMOVING AFT NACELLE TOP PANEL, STANDING ON WING, AND USING MIRROR TO EXAMINE AFT OUTBOARD CORNER WHERE MAIN FUEL LINE PASSES UNDER CABIN HEAT DUCT. SUBMITTER SUGGESTS EVERY SENECA I AFTER 1972 WILL HAVE THIS PROBLEM. SOLUTION: BEND FUEL LINE AWAY FROM DUCT, INSPECT AND PROTECT.