I have an issue with the rudder servo on a plane I just purchased that has me scratching my head, need some help.

If I take the rudder stick and deflect it right or left a little, then let go of stick, the rudder returns to center as expected. If I take the stick and fully deflect the stick to left, and then let go of stick, the rudder returns to a point that is about 20 degrees to the right center. Then, if deflect the stick ful right and let go, the stick returns to dead center. Power is coming from a fully charged LiFe battery.

All other servos act normally.
Tried 3 different rudder servos this afternoon, same result
Replaced servo cable between receiver and tail of plane where servo connects to it, same result.

You have a binding pushrod, hinges or something else in the system. Disconnect the linkage from the servo and move by hand to feel the bind.

Make sure the servo mount is not loose and moving a little.

Disconnect the pushrod at the servo and see if it does it. Though not likely, you could have a bad stick pot in the radio.

And one of the most obvious...a cheap servo. Don't chase your tail too long on the issue.

Kurt