Guys that race dirt have this issue. The dirt gets build up behind the buttons causing them not to move. If you race dirt, this is most likely the issue. My friend took his apart, cleaned it with Kal-Gard Contact Cleaner and a river of dirt flowed out of it.. You can also use, I think, a product at Home depot or lowes sells..cant remember the name...

Once he got the debris out from behind the buttons, it worked fine.