The slop in your servo is somewhat similar to your gear mesh with the motor. Too tight, and the servo will bind, too loose, and the servo will strip gears. As metal gears in a servo wear, there becomes more and more slop.

Another thing to consider is what servo horn you are using, which you are using an aluminium horn, and check the slop in that. The servo mounts are another thing to consider with slop that apperently comes from the servo, and how tight they are on the servo.