As said above, it depends on if you are to run it into the ground or not. If not, it might be a pig to sell. I would only get one to run to death personally, but I see no real problems with a CAT D on a relatively old motor. Assuming it was done while the motor was old.
I have heard, from a work acquaintance though, of someone who had an accident in a previous CAT D vehicle, and the insurance wouldn't pay out on the car (third party was okay), because it had already been paid out on. Not sure how much I believe that mind.