What was found
(CAN) DURING FORWARD FLIGHT WITH UNDERSLUNG LOAD AND SIGNIFICANT NOSE DOWN ATTITUDE FUEL ODOR WAS NOTICED IN CABIN. ACFT WAS RETURNED TO BASE AND GROUNDED FOR TROUBLESHOOTING. TROUBLESHOOTING WAS COMMENCED LATER IN THE WEEK AND FUEL VENT LINE LOCATED IN VERTICAL CONTROL TUBE TUNNEL WAS SUSPECTED TO BE LEAKING. VENT LINE IS A RUBBER LINE WITH METAL BRAIDING ON THE OUTSIDE, DATE OF MANUFACTURE WAS 1995 AND EXTERNALLY LINE APPEARED IN SERVICEABLE CONDITION. LINE WAS REMOVED AND TESTED FOR LEAKS ON BENCH. LINE WAS FOUND TO BE LEAKING FROM RUBBER INTERNAL LAYER IN MULTIPLE LOCATIONS AND APPEARED INTERNALLY DEGRADED. THE NOSE DOWN ATTITUDE OF THE ACFT RESULTED IN FUEL TRAVELING UP THE VENT LINE FARTHER THAN IN NORMAL FLIGHT AND THIS CAUSED DISCOVERY OF THIS LEAK.