9000 series are pretty well known to be weak in the rear end, and some in the trans, that's why deere wouldn't warranty them for pan work. They also have frame breakage issues with the front frames. In normal ag service they're probably adequate, but for any kind of heavy duty service, at least the old ones were a no go. At local JD dealer sale, one last year had front frame welded in 2 places with less than 3000 hrs. One this year had both rearends redone, announced at the sale, with less than 4000 hrs, so I'm not dreamin it up. As for the STS's. I know of 3 personally that have had the rear axles fall off. One other one that was leased out never did have the header height control work right. Can you imagine running a couple thousand acres of beans running a 30 ft platform by handIJ Using frangible material in the threshing area isn't the brightest idea either. They are fine machines, but by no means without their bugs. Chads