I'm a tech at a John Deere dealership with about 12 STS's in the field. Since they have been out, we've only had to remove a rotor once on a combine that was sold first year they were out. The machine had alot of hours on it the first season. (about 750,000 bu. of corn in one season) The reason we pulled it was that Deere harvestor works wanted to come out and take measurments of all the rotor componets. Granted, we dont have any rocks in the fields here in this area of Nebraska but I'm trying to think of a reason you would have to pull the rotor other than a rock for something like running a steel post into the rotor. The only rotor repair we've had to do since we've been able to do easily without removing the rotor. PS. I grew out running a gleaner combine (a little F2) and will always have a soft spot for silver combines.