Filiform on newer AS?

[NWGreyhound]

I have a 2010 25 FC. skin remains in mostly new condition except for two small areas (2 sq in ea) that spread out from under the rear exterior light fixture. I haven't taken off the lights yet but suspect they start at a hole drilled for screws.

What would be the best strategy for repairing these are stopping their spread?

Lou

[Tilemaker]

Corrosion X stops the filoform corrosion. I'd use rubbing compound to remove the filoform and the apply a light film of corrosion X regularly