[Flyinfool]

Flutter is not likely to be a servo problem in a heli.
Blade flutter is usually a mechanical problem.
I would start by checking the dampers and the blade grip bearings.
Worn dampers and/or grip bearings are the most common cause of blade flutter.

Flutter puts a lot of stress on parts and could have damaged any or all linkages from the grips to the servo, check them all carefully.

Once you get a flutter, check your spindle to be sure it is still straight, I used to bend a spindle every time I had a blade flutter on my R50.

As for the tank, If the tank has a leak, get a new one, I never had any luck trying to patch one. Check your frames where the tank dimples seat, and use some fine sandpaper or Exacto knife to get rid of the molded in sharp edges that will cut the tank.