That's a common problem with newer S3's
Have you had it out in the rain much?
Water bleeds past the console seals and rusts out the buttons on the circuit board.
Both outside buttons went on mine.
The good news is that it's covered under warranty (AU$1200 for a new console), and when you swap it out, the odometer starts off at zero again!
I finished off the summer season, and then put it in the shop for a replacement. Wound 9,500km off...
Congrats.
