I ran across this thread while searching for more information on Nicca rangefinders. I have a little bit of experience dealing with 60 year old shutters, so I thought I'd pass it along.
I bought a Canon IIIa rangefinder a few years ago, and the first roll of film I ran through it revealed that the shutter had pinholes. Like about a dozen of them. I don't recall where I read this tip, but I tried it, and it works great. There's a product you can buy at the big box stores and elsewhere called Plastidip. Its a liquid polymer of some sort that was originally used for applying an insulation coating on tool handles. You dip, say, a pair of pliers' handles in a can of this stuff and it will leave behind a wet coating on the handles that will dry to a pliable surface, insulating the handles from accidental electrical shock. It comes in a variety of colors, including black. It's also available in spray cans.
So I bought a spray can of the black Plastidip to try on my IIIa's shutter. I sprayed a couple of second's bursts onto a paper plate, and then using a medium stiff artist's brush, I reached through the lens mount and carefully daubed the Plastidip onto the shutter curtains. I'd apply it to the first curtain, wait until it dried, then I'd trip the shutter and apply it to the second curtain, then let it dry again before I charged the shutter. The key was to apply the Plastidip in a thin, even coating. And to apply additional coats sparingly, as necessary. This last bit is important because the Plastidip has mass and adding too much mass can change the timing of the shutter. So, easy does it, and all that.
Anyway, after this first go-round with the Plastidip, I took the camera out and shot another roll with it. It still had pinholes, but they'd been reduced from about a dozen to a couple. So I gave the shutter another treatment, then ran another roll through the camera, and this time I was successful. No more pinholes.
Because of Plastidip's properties -- it stays flexible indefinitely and stays where you put it -- this is a permanent repair. And fortunately , it goes on thin enough such that its presence is almost invisible.
Since then, i've used it on a couple of other repairs and it's worked well for these. I don't know what it is about Metz's coiled flash cables, but they tend to rot after they get old, and the external insulation cracks and falls off. To repair this problem, I sprayed the cables with Plastidip, which did a good job of coating them. To all appearances, this was a permanent repair.
I haven't tried it for this yet, but I'm thinking that this repair should also work welll for pinhole repair on camera bellows. Hey, why not. It's flexible, and can be applied to build up to any thickness desired.
