My friend Bill has an Avid with the integral fiberglass fuel tanks.one of them developed a leak after four yrs, we removed the wing, peeled off the fabric under the tank, cleaned prepped and patched. Now four months later it is leaking again.
I am suggesting sloshing sealer, I've never used it, read about it, so of course I'm an expert. Not.

Any experts out there who have used it and success?

Thanks

Ray