Is it the actual switch, or the plastic. The plastic wears. I had the same issue and just heated up the tabs so it was hitting the switch right. It was supposed to be a temp fix but still works so I never ordered the replacement.
Unplug the machine first. Take the case off (pretty easy even if you are not mechanically inclined). Pull the plastic peice off for the cursor buttons. Plug the machine in, turn it on, and touch the micro switches. If they function, you need to replace the plastic peice. If it doesn't, you need to replace the switch.
The plastic peice is easy to replace if you got that far. The switch takes some skills in electronics so I would send it in. Test it first at home if you know how to turn a screwdriver because it may only cost $5 for a plastic piece.