The 67, and its earlier incarnation, the 6x7, is certainly getting on a bit in terms of age. and many, many of them the world over have seen lots of service. It's a bit of a risk to just plonk money down on any one assuming it has been well looked after, but good specimens can be found. Models date from 1969 to 1989-1990 (when the updated 67 came out). How they are treated plays a role in reliability, especially if the shutter curtain is prodded, or somebody has carried out mechanical probing of stuck mirror (easily reset without physical coercion!). I avoid any camera with pronounced dents or damage, especially to prisms (and dents and scrapes are common on 6x7 and 67 bodies that have been in professional service). There's not much electronics in either camera save for the TTL meter prism. I guess like old dogs they will hobble along til the very last, faithful to the master before expiring midway through a precious roll of film, and thus you beginneth a fumblefest, in a cold and dark place, to extricate your prized film from the beastie without incurring any trauma to
that big shutter curtain... Things like light seals around the back cover and TTL prism can be done yourself with light seals readily available ex USA on eBay.
It has been reported that if the shutter is left cocked for a prolonged period of time, then shutter speeds will become inaccurate. So obviously it's a good idea not to mothball a 67 / 6x7, but put it to good, solid use and look upon it as a faithful servant, probably with a long and adventurous previous life.
I purchased my 67, minty, from a deceased estate in California (so a looong flight to Australia!) and was told by the dealer that it had received very little non-professional use. Michaels Cameras had a 67 in good condition but it had a jammed shutter and scratchy winding lever. But I was after the 90mm f2.8 attached to it: unfortunately, I was not successful in persistently arm-bending them to part with
"just the lens, please!"...
