If it's like most mice, it all should come apart easily with one or two screws. I wouldn't put water through it. Isopropyl alcohol from an aerosol should blast out the switch contacts and clean the sugars off the sensors. Was it a ball or optical mouse? An optical mouse might just need some cleaning of the lens, otherwise the ball mouse will need cleaning of the detectors and bearings.
don't forget to see if there's any build up on the hinging parts of the buttons.
At least if it continues to play up you can just pass it off as a drunk mouse.