"an interesting experience involving a mud-dauber who thought my left wing
tank vent was the ideal place for, well, mud-daubing..."

I have a simple fix for those with NACA style fuel vents.  I cut a piece of
1/4 inch thick Scotch-Brite abrasive (fuel resistant, the green stuff you
use to scuff aluminum) into a rectangle, and then tucked it into the fuel
vent behind the lip of the NACA scoop.  It is fine enough to keep out the
bugs.  It has high porosity allowing air to flow through easily.  And the
large cross sectional area in the NACA scoop prior to the transition to the
round vent tube is more than large enough to assure negligible air flow
restriction.  

Air flow, yes!  Bugs, no!

Fred Moreno