[JAG]

What year is the aircraft (1968?)? My 1966 has a fairing over the gap, with a small rubber channel on the edge that goes against the fuselage. This is the same set up for C337s up to 1973. I can't quite tell from your photo if it is only a rubber seal between the wing and fuselage, so I cannot tell you if there is a problem. The fairing could be homemade, damaged, etc, so the only way to tell, is to remove it and look at structure to determine if there is a problem.

Regardless, anything that fills the void between the wing and fuselage is primarily for aerodynamics. The fuselage penetrations would be normally sealed where any fuel lines or wires go through. It is best to have a great seal on that fairing as the more moisture you can keep out of that area, the better. You have some flight control cables and attach fittings that you want to keep dry. Typically those rubber seals on filet fairings are easy to replace. New seals are available from various suppliers - use a little contact cement or Gorilla Glue (my preference) to glue on fairing.

Jeff