The question missed by everyone: How big a gap and what type hinges?

You can get away with a 1/4 inch gap (a bit extreme) if the hinges are solid, preventing a floppy hinge line. You can't get away with 1/8 inch with CA hinges, as you wll have a floppy hinge line, introducing a way for flutter to get started.

The gap sealing is MORE for improving the control responsiveness than for flutter prevention. It also reduced drag a tiny bit.

So... if you can easilly move the TE of the control surface without moving the servo... you may need to rehinge it.