Thanks kuzano for this information. I might go see the camera this weekend.
I'm sorry to ask you this, but there was something that I didn't understand from what you said, don't worry... it's just because English is not my first language. It's about the "moving cloth dark slide", by this you mean the curtain that protects the lens from the inside?
As Sevo said, the dark slide I spoke of is to protect the film against the light if you are changing the lens to another focal length while a roll is in the camera. Frankly, I do not test the fates on this. The continued operation of the dark slide is the weak link in the Big Fuji Rangefinders, primarily due to age and diminishes spring tension rewinding the cloth slide.
The dark slides demise won't cripple the camera in any way, and since one is usually only shooting 8 or 9 shots per roll, mid roll lens changes are not all that necessary. I've had plenty of the interchangeable lens Fujica's and found them to be robust and reliable, in spite of non-working dark slides. I simply don't use then, and when I get another Fuji body, I may never know if the dark slide works. I generally don't test it, or find a need for it.
It's much like trying to use self timers on old folders... a much worse problem since self timers have sidelined more old folders than most other problems.
As I mentioned, I will probably never sell my GL690, and you may easily feel the same with the GM670, IF the format suits you.
One thing different about the GL and GM models over the G690 and bl models. The GL/GM bodies have two shutter releases. One on top for standard horizontal use, and one on the front to facilitate holding the camera in a portrait mode.
As some say... simply more to go wrong.... sorry for that rationalization folks, but I've never had a problem with the second shutter release, and it has facilitated easier shutter release when shooting portrait.
Your new GM will be the latest interchangeable lens body sold, and will have the second shutter release.
Good luck and enjoy. I've been using these big heavy Fujicas almost since they were introduced. One thing about Heavy and the in lens shutter. No shake when you push the release. It's a "resistance to inertial change" thing.
I repeat from my first post. You are paying $350 for the body which is fair, and getting a $300 to 400 lens for free.