I was having this problem on my '09 250XC...granted, this has the old "restarter" motor for 2-strokes, but the 2012 starters probably operate similarly. The starter would work most of the time, then some of the time, and finally none of the time. I pulled the electrical connector off the starter, hooked it to a volt meter, pushed the starter button and confirmed that the right amount of current was making it to the starter motor.
From there, I went to Slavensracing.com and began watching their series of videos on rebuilding starter motors. Best I can tell, the problem was a broken brush spring. But I bought the whole Slavens rebuild kit and the starter works just fine now.