you can reduce for example the tolerance of the one axis beside the long slot with the sheet of this
http://www.klangspiel.ch/boat_bausat...126_093150.jpg
No joke. I´ve done this tweak and it works very good. Fix it with glue on the opposed side (hotglue). I´ve lost the cable of my camera so I cant make photos of it.
the other thing are the potentiometers. there is a very expensive alternative called hall sensor or a cheaper but 1000 times better alternative as the original plastic pots. Look here:
http://leobodnar.com/products/BU0836X/p260.pdf
I got 3 of the p260 model. They are steered with a servo horn for throttle, x and y axis to gave them a working degree of nearly 170°. the smaller the servo of the pot in relation to its opponent the bigger the working area. Its similar to this
http://www.wingsofhonour.com/hardwar...090718.en.html
I hope you can follow my horrible english
edit:
looks messy but works. The good thing on hotglue is you can remove it completly or adjust all glued elements.