This is becoming a very common problem on 850's. Unfortunately, the dealer will tell you that the only thing he can do is replace the entire instrument cluster, at substantial cost. The problem, though, is one small gear that strips in the odometer. A replacement part can be ordered (see http://www.odometergears.com/ for one source) and you can do it yourself or have an indy do it. Getting to the back of the cluster is not trivial, but it's not all that hard either. See Bay13 for instructions.

Gerald C