Here's some more information to gather: Have you tried KE rolling in each direction so you have used both right rudder and left rudder? Could the pushrod be buckling in the pushing direction and work fine when it is pulling? How does the servo/pushrod (rudder)surface behave if you (on the ground) move the stick and resist the movement of the surface with your hand (especially in the direction you have had the excitement)?

I'd be intested in knowing what you find!
Tom