I called Mamiya and asked about this back. The representative said they didn't sell very many of them. Apparently, it wasn't very well received in the market place. Rumor has it Mamiya wanted to compete with Fuji that had 6x8 capability. This is more like 6x7.5. Really not worth the effort....

I keep trying to get a working 6x7 back. The last one I got, an SD type with near mint condition had light leak. Non SD type with foam seal were a mess.