I had a KZ1000P police bike. I got it after it had been put out to pasture by a suburban Cleveland police department. It was old, tired, ridden hard and put away wet. I got it cheap and the only thing I did to it was to correct some of the wiring leftovers from removal of the red and blue lights. I rode the piss out of it for two seasons, only changing the oil occasionally. Aside from riding a KZ off a cliff I don't think you can break one. They are substantially over-engineered, just like their brethren Suzuki GSes, Hondas, and Yamahas of the same era. As long as the previous owners have not screwed with the carbs or the wiring you can't go wrong.
"Keep on 9-in"