Quote Originally Posted by Ulophot View Post
Better analysis than I had come up with, no surprise to me. I'll see what these tests yield, though I have no long lens, just a 210 and 135.
Doesn't matter, you don't need to make a photograph to test for leaks. On the contrary, at this stage of the investigation it would be better not to. Just plug the front standard with either of your lenses on its lensboard but with the shutter closed and lens cap on, take the camera out into bright sunlight, extend the bellows as far as it will go, insert the film holder, pull the darkslide and let the camera sit for a while. Then develop the film or paper to see whether and where it's been struck by light.