Some buttons no longer working

I’ve had my Sansa clip zip for around 18 months, and the left/previous track button has stopped working along with the down button. They do eventually work if I keep prodding, but barely respond.
Is there any fix for this? I’ve managed to get the back off but don’t know where to go from there.
The device is rockboxed and works fine other than this minor inconvenience.

Hardware issues such as this are rarely ‘fixable’. Sounds like it’s time for a new player, but you might try re-applying the firmware in case it happens to be a firmware snafu.