The motor on the PT425 is a Kohler. There are several Kohler certified shops around here. All of the hydraulic pumps and motors could be serviced at any good hydraulic shop(several good ones around here as well). Same goes for hydraulic hoses, rams, valves and linkage. The tires, rims, electrical all seem to be standard stuff carried at local parts stores. Everything else is plate steel. The machine is really very simply constructed out of heavy standard parts. I can't say enough about how tough it seems to be built.
However, I would strongly recomend that you test drive one, as well as JD, Kubota, NH and several others. Look into service in your areas on the parts I mentioned. Make sure that the machine will fit your present and future needs.
Why the PT422 instead of the PT425? Just curious.