Yes, I have sealed the hinge lines. As a result of this experience with flutter, I am
(1) Never going to have mechanical advantage worse than 1:1 on any control linkage.
(2) Always going to seal hinge lines
(3) Going to use pinned hinges instead of fiber.
My next plane is going to be scratch built, and it will probably have some carbon fiber strengthening.
Thanks for you good advice on mechanical advantage etc.