I don't think it will be as difficult as you think to get a good copy of this lens. And if I recall, I remember reading somewhere that the lens could be calibrated... My copy is good. Works well and is a flexible lens. Not nearly as good as any of the D series lenses.
That being said, This lens is not my favorite. It works well for me when I need to use it, but it's not a lens that I reach for---it just ends up being used because it is the only one handy, and gets the job done. (I wouldn't use it for advertising and products, though)
Maybe it is a bit harsh for me to describe it as the Denny's of Mamiya lenses. You never go out to eat at a Denny's restaurant. You just end up there because nothing else is available at the time. You eat, you're satisfied, you go back home. Done.