What was found
OWNER STATED ONE VALVE WOULD NOT OPEN AND A 'GREENISH STICKY' SUBSTANCE WAS FOU ND IN THE OTHER. REPLACED BOTH WING TANK DRAIN VALVES. CHECKED AND CLEANED ALL FUEL SYSTEM SCREENS AND FILTERS. NO DEFECTS NOTED. DRAINED 5 GALLONS FROM EACH TANK, NO DEBRIS NOTED. EXAMINED VALVES, O-RINGS APPEARED TO HAVE DETERIORATED. ALSO, POSSIBLE THAT SEALING COMPOUND FROM BLADDERS MAY HAVE BEEN THE CAUSE. BOTH BLADDERS WERE REPLACED RECENTLY (1 NEW, 1 REBUILT).