Hi Larry,
I would be absolutely lost without my beloved KN7000 and like Bob, I have purchased a second KN7000 as an 'insurance policy' just in case..........

Like any piece of electronic gear, it is almost impossible to say how long it will last before giving up the ghost. It would seem that your experience with your KN7000 was typical of the 'Bathtub Effect'

Quote "The Bathtub Effect is shown as a curve on a graph, depicting the failure rate of a piece of equipment over time. The outline of the curve typically assumes the shape of a bathtub. In the initial phase the failure rate is higher, becoming progressively lower as the equipment is worn in and faults are mended. The curve is then flat until the equipment begins to breakdown again at the end of its normal working life".

Bob's recommendation of unplugging from the mains supply is certainly a good precaution. I don't do this myself but I do use a surge protected extension lead, through which my KN7000 and its associated computer equipment is connected to the domestic mains supply.
The only minor fault which I have on one of my KN7000s is associated with the Start/Stop button, which occasionally fails to operate correctly. It is just a switch contact problem and doesn't worry me too much, since I just use a footswitch instead.