When I purchased my Zone VI (Tachihara) on e-xxx several years ago, I was disappointed to find that one of the knobs was not working properly. After making several posts on this and other forums, I finally decided to follow other's advice and contact Jim at MPEX. Jim answered my questions and stated that he would check his inventory or contact Tachihara to see if he could get the part.
Jim responded the next day - MPEX had the part in stock. The knob arrived today and, finally, the front rise on my camera is tight.
Thanks Jim and I hope we can do business again soon.