Are you absolutely sure that it's the servos that have the movement in them, and not the servo arm/linkages? Many times when control surfaces start developing slop in them it's because the linkages, servo arms, or control horns are wearing out. As the parts wear out they develop slop in them which results in the movement that you describe. One of the worst spots for wear is the holes in the servo arm, they will wallow out and allow movement in the linkages. Check all of this out before deciding to replace the servos. Many times replacing some or all of the linkage components will remove the movement and return the control surface to "like new" condition, and you won't have to replace the servo. If after you have checked all of that and you still have the movement then you can indeed look at replacing the actual servos.

Ken