Have a neighbor farm who operates 2 8640s.  Both have close to 10,000 hrs and just had new engines installed about 1,000 hrs ago.  Neither one has given them much trouble.  The other one is off to the right of the picture hooked to a Flexi Coil sprayer.  They would not be my first choice for a tractor back then and now but the way some people talk about them, they fall apart before they get to the field.