On Sunday, 5 November 2017 23:45:19 UTC+2, wrote:?

Flutter was associated with seal tapes. Flaps fluttered more than ailerons if I remember correctly.
UH

Mine had aileron vibration (it is not flutter) twice with pristine teflon/mylar seals, so it might not be that simple. I did change flap hinge bearings and new seals just to be sure and never experienced vibration again. (Control play was well within limits before change).

Talking about 20 handling, you would probably compare it to gliders similar vintage. LS4, Discus or Ventus with aft c/g will spin as eagerly and drop wing in most cases in similar fashion. 20 is no different in that respect. I flew 20 for over 1000hrs with few wing drops after mishandling the glider in thermal but I wouldn't call the glider anything but extremely well-behaved. It is the safest glider to land in tight spot. One of few gliders that truly were well ahead of it's time.