The Kubota diesel engine
itself is used for all sorts of applications including tractors, boat
engines and generators. For the engine rebuild
I would try a tractor dealer, bound to be cheaper than a genuine marine mechanic
Either way, I would get a quote for the "top end job" from a Kubota mechanic
of some kind, marine, tractor or whatever. Double that quote. Add it to the price
of the used generator
and if that total isn't 25-50% less than a new unit, walk away.