You guys finally made me to shake the dust off my copy of Martin Simons book, Model Aircraft Aerodynamics, 4th Ed. Here's some excerpts from it, with due credit given:

(p 180) To prevent flutter it is essential for the hinged surfaces, especially on fast models, to be without slop, and for the wings and fuselage to be stiff. Secondly the control rods and cables, and all their linkages, should be free from play and again as stiff as possible. Finally, the control surfaces themselves should be as lightly built and stiff as possible, and where possible, mass balanced

(p 63) Serious losses occur if there are gaps through the wing at any point. Through such gaps the air flows from the high to the low pressure side of the wing, creating turbulence and reducing lift. Control gaps have similar effects and all such leakages should be carefully sealed

For what's its worth. Well at least, I have made good use of my book