We have a MT 855 that we bought new in 2005. Over 10,000 hours on it now, and outside of tracks, less than 10.000 bucks in total repairs over its life.
Mid wheels, hubs, and bearings have been the main problems, but then again I have a lot of rocks. Clear View caps really cut down on the bearing bearing problems. Have replaced quite a few serpentine belt idler pulley bearings as well.
Cab is too noisy and too dusty (doesn't seal well). Other than that, best tractor that's ever been on this farm.