Hi,
One thing you could do to reduce the slop, if you have not allready tried this, would be to set the servo travel to maximum in the transmitter and come in on the servo arm to get the right deflection. The servo will still have the same slop, but coming in on the arm will reduce it at the surface. This will also increase the power that the servo can apply to the surface, increase the position accuracy, and improve flutter resistance.

Hope this helps,

Steven