I have a 2009 RMK 800. Ran great until just this last winter. Wasn't getting the top end RPM at elevation. Tried different things, then was told to try a lighter spring in the exhaust valves. Pulled the valves and noticed scoring on the piston on the mag side.
So, I fixed 'er up and and we will see what happens this winter. Note that prior to this, I had all the fixes done, and the most current flash. So it's hard to say if it was the 'old issue' or if it was me, or something else. It seemed to run just fine, just no top end (would no go above 7500 rpm). So, I say buy it but just keep an eye on it so you can catch something (if it happens) before it causes catastrophic issues.