Hi All,
I got 2 Esploras for Christmas, both purchased at Radio Shack. One had a joystick button that fit (larger internal, D shaped hole) and one that did not fit, exactly as illustrated in the post. I used a drill bit and carefully drilled out the one with the too-small hole. Alternatively I could have exchanged it at Radio Shack. In either case, the joystick did not 'snap-on' so I used a very small amount of white school glue, which if used sparingly is not permanent but holds firmly for as long as you want. Once you have confirmed the joystick button fits or you've carefully drilled it out, flip the joystick button over and apply a tiny drop of white school glue. Then flip the esplora board upside down and insert it into the button. Let it dry upside down to prevent any glue from leaking down the shaft into the joystick mechanism.
KB