Leaking Fuel Tank

  I would suggest removing all the trim around the tanks so you have full access to the tanks and fuel lines, drain the tanks and lines, then pressurize the wing tank system with low pressure air (mouth pressure is enough), then brush all the joints and seams with soapy water and watch for bubbles. This photo is of me testing my fuel tank for leaks. The rubber glove (I didn't have a balloon) acts as a pressure regulator so I don't over pressurize.

My 415C, N3779H, Serial No. 4404 is leaking fuel from the right side wing tank.  It only leaks when the tank is full and stops when the tank is down to about 2/3rds full.  Also noticed some light fuel trace on the fuel line and shutoff valve on that side when it appears to be leaking.  Leak is occurring when the plane is parked in my hanger.  Fuel consumption while flying is in the 4.5 to 5 gallons per hour range.

Any comments/suggestions on this issue would be appreciated.