Oiling Fuselage Tubes

Main places I see are the longerons at the D windows and the lower longerons. The dirt gets between the fabric and the longeron and acts like sand paper and a wick for moisture. The U channel forward of the right D window that makes up the flip up window frame that is stitch welded to the tube is the biggest culprit on the Super Cub.

Tubing and structure under battery is another one along with anywhere rodents have gotten in and nested.
Lower longeron under the battery box.

Upper longeron under the D Dindow behind the fabric headliner where a bird had built a nest.

D window corrosion after sand blasting.


Lower longerons after blasting.