Ummm, there's a regular contributor here, paul RON, who uses/services RB/RZ cameras. Simply do a search for his user name and i'm certain you'll see many, many of his posts which illustrates his technical knowledge - i'm sure he can help you out. Oh btw, it seems he's exceptionally well-versed on all the Mamiya RB/RZ lenses and their maintenance (in addition to the cameras....).
It's good to 'take care of our own'...... especially when they add so much to our Community gratis (in the way of information, etc).