Better motor control.
Timing: assuming rigidity of linear position is crappy, allow more time for it to bounce back.
Speed: ramp-up speed in one direction may be different from the opposite direction.
Position: accuracy of RC servos is almost not worth measuring, so many companies haven't. But you can hack it (via contact switch and something that juts out) to add a simple shaft rotation encoding and correct when needed.
Software correction: draw a grid of straight lines and adjust drift in software until it looks like a grid.