I bought a used Orion XT10g and the ESC key didn't work on the SynScan hand controller. It turns out the underlying electrical contact pads had some corrosion or dirt on them. I used the old technique that I used to clean slot car contacts. It's pretty easy. You'll need a skinny Phillips head screwdriver and a pencil eraser.
WARNING: Be very careful because taking this apart could break something.
1) Flip it over and remove the six Phillips head screws. Then remove the back half.
2) Remove the two Phillips head screwdrivers that hold down the end with the RJ6/phone jack connectors (circled in yellow).
3) Carefully lift up the circuit boards from that end, tilting them up so you can see all of the gold contact pads.
4) Use a pencil eraser to gently clean the pads pertaining to the button that no longer works (see red circles for the ESC button contacts).
5) Just reverse the process to close it back up, being careful not to pinch any wires.