A crack in the wood structure that connects servos and ailerons or other control surfaces could have been developed during the crash.
The structure works as part of a push-pull system, as counterpart of the linkage and servo.
A strong linkage plus a weak structure base equals a weak system.

Feel how firm each surface is when you try flexing it by hand.

Also, servos may be worn out the gears in these years.

I believe that engine vibration and flutter are not related.

The only good solution that I know is balancing the control surface aft and forward the hinge line:

http://www.centennialofflight.gov/es...rol/TH28G5.htm