Ok, let's debunk this myth right now...

Sealing a gap has nothing to do with stopping flutter. In fact. sealing a gap can even CAUSE flutter.

The reason for sealing a gap is to give better control surface response. Nothing else.

Look at a flag waving (A flag waves due to the exact same principles that cause flutter). There is a gap between the flag and the flagpole. If you seal that gap will the flag stop waving? Of course not.

If you want to prevent flutter, use strong servos and avoid having any slop in your linkages.