The cap for the fuselage fuel tank (which can apparently hold 50 U.S. gallons)
above the "F" on the port side of the fuselage just below the canopy.
The stencilling notes that it is "Suitable for Aromatic Fuel."
"Aromatic fuel" does not refer to the fact that all gasoline is foul-smelling
but rather that high-performance engines can achieve even higher performance
through "aromatic" fuel additives such as benzene, toluene, and xylene. However, the aromatics could affect certain types of rubber, so special hoses and seals were required for use of aromatic fuels.