Not an answer but may make you feel better
John,
I can tell that I have a section like that on one wing of my RV-7A.
If you push on it it will "oil can".
It bugged the heck out of me. Now when I'm cleaning the belly I look at both wings until I find that section that bugged me so much and laugh out loud for worrying about it so much!
Mark
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Mark Burns
Ruston, Louisiana
RV-7A N781CM 1,650+ hrs
FFI FL-24
A&P
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