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Another take on the 'intermittent fuel smell in flight' problems

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Subject aircraft is a very well equipped V35TN, a real sweetheart.  Customer, from time to time, caught a whiff of fuel smell, then it disappeared again almost as quickly as it appeared.  We checked the usual areas, like fuel selector and fuel lines in the cabin, fuel flow line from the firewall to the gauge, vent line continuity, etc.  Found no tell-tale blue staining.  We asked the customer to note flight conditions, fuel level, etc., when he noticed it.  Seemed to be in mild turbulence, with tanks near full.

Well, annual time was upon us for this Bo.  We decided to change all the vent line interconnect hoses thinking that may be a problem in the aft wing roots.  As is usual for us, a different technician does the post inspection run-up and ops checks than the one that did the pre-inspection run, so it was David's turn.  After the run, he told me he was able to duplicate the fuel smell, and when he got out of the aircraft, there were a few fuel drips coming from the left fuel vent by the aft wing bolt.

In addition to the flow checks we had previously performed, we decided to pressure check that vent line:  Disconnected and plugged at the end of the fuel cell, plugged the flush vent, and applied low pressure shop air to the extended vent.  Sure enough, we hear air flow between the lower forward wing bolt cover and the cabin air inlet screen on the leading edge.  The video scope was put up into the wing root and nothing was found amiss.

After consulting the owner, the wing was removed to further inspect the line.  First thing noted was the poor job of installing the wing root seals; the retaining lip (supposed to go around the end rib to secure the seal) was basically cut off, and the seal was glued not only to the exterior skin edge of the wing, but to the fuselage.

There is a baffle attached to the inboard rib to keep airflow available to the pilot's knee vent from the leading edge intake screen.  Guess what David found sitting on the inside edge of the lower wing skin, just in front of that baffle?

Yep, that is a folded piece of rather aggressive sandpaper.  We kind of surmised the same rocket-scientists that put the wing root seals on, tried to open up the gap on the installed wing to get the seal lip in place, and 'dropped' this foreign object in the wing root.  When discussing what a foreign object can do, damage is the first thing that comes to mind.

Notice the abraded area below the cabin air inlet holes on the side of the fuselage?  Likely in flight, the sandpaper was flapping around.  What else could it have been flapping on... Hint:  Look in the mirror in the next photo.

Yes, that is a 'sanded through' fuel vent line!

A new section of line was spliced in.  The vent line and fuel return lines were both (successfully) pressure checked, glue-goo cleaned off the wing and fuselage, and wing installed with new crush washers and seal.

Another one for our 'Wall of Fame'.