Look up any of Richard Johnson's flight tests before and after seals, especially the LS-4. Or any other modern sailplane. There was as much as a 5 point difference.

Thanks. I read the two LS-4 articles, but the "after" wasn't conclusive: Different plane, different probe positions, and Dick doesn't make much of a conclusion on if the performance was better, or just measured to be better.

Is there another one where he does the same plane with the only difference the mylar seals?