Thank you for your replies. It is the modern Mamiya 6 rangefinder. Based on feedback here and elsewhere it looks like the final answer is Precision Camera Works. I called them yesterday and they offer an overhaul service which includes rangefinder calibration and fixes any issues for a reasonable price. Apparently they are the only official Mamiya maintenance shop in North America, and also have a large stock of parts. I'm pretty excited to send it off and get it back in action!
Thank you for your replies. It is the modern Mamiya 6 rangefinder. Based on feedback here and elsewhere it looks like the final answer is Precision Camera Works. I called them yesterday and they offer an overhaul service which includes rangefinder calibration and fixes any issues for a reasonable price. Apparently they are the only official Mamiya maintenance shop in North America, and also have a large stock of parts. I'm pretty excited to send it off and get it back in action!