All of the other buttons on my 05 are fine but for the last year or so the defrost buttons only work when the wheel is turned at least 90 degrees. I am guessing that there is a contact strip of some sort. How hard is it to get to the backside of these buttons?
One suspect part is called "clockspring" or "spiral cable" and is subject to breaking. Search for those topics and there will be some pix to help. Individual buttons can also fail, but it will take some probing around with a continuity tester to decide which is the culprit.