Yales are good trucks - like all they have issues but w/your TLC they can go the 10-12K w/o much problem.
My only concern is the coolant lose issue - as you know well it doesn't just evaporate & if ain't on the ground then it is a good chance to find its way into the combustion chamber via head crack or or blown head gasket. The Mazda does have an aluminum alloy head that are prone to blow gaskets from time to time & crack head - especially after or during summer time.
If this is a new service customer Congrats (as long as they pay promptly)