I had a very similar problem with the transmitter unit for my realflight sim. This is also made by Futaba. I can't remember what the problem was, but I do remember that I took the back off and compared it with the other stick. It was an easy fix.

If the radio is under warranty I would have it repaired. If not, I don't think you will find it too difficult to fix.

Let us know how you get on.