I've not seen such a washer on my 2.8C Xenotar. Or behind a 2.8A Tessar, or behind a variety of 3.5 Tessars and Xenars. No washer behind the front lens group on any Minolta Autocords or YashicaMats, either. Or Zeiss Ikonta Tessars.
Have you simply removed the washer, screwed the front element back in as far as it will go, and then made shots? Every lens I have ever disassembled that goes on a leaf shutter like a Synchro-Compur has the front and back blocks simply screw onto the shutter body without any washers or spacers. Proper lens spacing is designed in to the mounting, not adjusted by washers or such.
That washer looks like one that would go behind the shutter. I'd have to dig out some notes, but I think that there is usually a brass one to the front side of the lens board and a blued steel one to the back side of the lens board captured by the rear retaining ring/light shield (you can see this as a ~15mm(?) tall tube inside the camera).
There are repair people out there who would probably give you a simple yes or no answer with some better photos and explanations of where you found the washer. Most of the ones I have dealt with are helpful people who would understand your location and problems with shipping and might provide a simple yes/no answer as to whether they have ever seen such a washer in the position you describe.
Last edited by Dan Daniel; 05-02-2013 at 12:07 AM. Click to view previous post history.