We've gone through several of these remotes, which always fail in the same way within a year or two -- unit stops responding to the most used buttons.  This time, I took it apart and did two simple things.  I don't know which one fixed it, but it works now.  First, I saw some oily stuff on the circuit board under the buttons that don't work, so I cleaned that and cleaned the backs of the buttons.  The board also seemed very flexible, so I forced some styrofoam into the compartment behind the board in the area of the button problems, just enough to keep it from flexing.  Works great now.  I hope I never have to buy another one of these because they're getting impossible to find.