Hi.
Sorry to hear about your incident. You can consider your self lucky as flutter on a jet normally is fatal.
I have flown my Viper Jet (first series) for two years w/o any flutter issues at speeds upp to 330km/h on a regular basis (130N or thrust).

In my opinion the elevators and rudder of the Viper is sensitive to flutter if you don't take any precautions. By mass balancing the elevators (approx 20g in each tip of the elevators) and similar to the rudder you will reduce the models sensitivity to flutter.

The wooden part that came loose may be a secondary effect of a self induced flutter. The forces of a flutter when your jet is doing 150mph can easily rip out the servo of the elevator or fin or destroy a nylon gearbox of a servo. Always use metal gearbox.

I know the Mark II is a bit tail heavy an you may not want to add 50g of lead in the tail. However, if you do a proper mass balancing you can operate the elevators and rudder with a 24g Digital wing servo (Hitec HS-5125MG or JR DS161).

It would be useful to se a picture of the servo installation in the horizontal stab. Please check if the servo has come loose.

Also very important is to have a rigid an slope free linkage/control of the control surface.

/Johan