Corrosion fix
I have restored a number of aircraft & had to deal with corrosion. I would remove the flap, remove the stainless tape and check for more corrosion not only on the flap but also the rear spar. Strip the paint over the corrosion, scrub it with scotchbright & Alumiprep acid etch until the corrosion pits are clean. Flush it with plenty of water to neutralize the etch, dry it thoroughly, alodine it, then prime and repaint. This is a lot of trouble for one small spot but it is the best fix and I have done the entire interior of a Cessna like this over 18 years ago and it remains free of corrosion today.
Dick DeCramer
RV6 N500DD
130 hrs
Northfield, MN