I can take a flashlight,and shine it onto the back from the lens standard (without the lens, of course) and I can see light flashes through a small space at the corner of the grafmatic - it just doesn't seat flat.
The holder seems to be flat, it just doesn't sit 'deep' enough.
A two-sheet holder does not have this problem - I just finished running a few more tests, and no fogging at all. I rotated the camera through all the motions, making sure sunlight hit all parts of the camera.
Barnbaum uses Gramatics with a Tech IV as well, and he doesn't get light leaks either....
Me? I'll stick with cut sheet holders for now.