Bronica S2(A?)--1 Light Leak Out Of 12

What do you think caused this one light leak in one photo of 12? Is it possible the back opened slightly after I put the dark slide in maybe a little too hard? I didn't feel the back open but maybe it did slightly and closed? All the rest of the photos came out fine--sharp lens!

One of 11 that came out fine:

1st thing we always ask is, does the leak go into the rebate? That can tell a lot.

It does not look like a dark-slide leak, the do not usually go across that uniformly. Maybe a back hinge leak (if the leak extends into the rebate)

Here is the negative with the edges showing the leak:

There was another similar leak after the last frame--not in the image. This is the last frame:

It looks like a light leak in the film back (magazine). Accidentally opening the door would cause a more random, general fogging.

In your 'last frame' image, I see a line of fogging 2/3 down, over the '3' at right. It could be light hitting the camera at a certain spot; bright sunlight will naturally produce a stronger streak whereas softer light produces a softer, less noticeable loss of contrast.

If it only occurs occasionally, try and reproduce it so you can trace the leak's source.

Does it occur at only certain points on the roll? One of my Yashica TRLs had a light leak striking the film near the feed spool that only showed up on the first few frames of the roll, after which the film changed position and moved away from the leak.

Since it goes out on the rebate, it does not originate from the dark slide or the camera-filmback interface.

By the shape, it likely comes from the seals on the film back's door, and by the shape of it, probably the top or bottom edge of the door. The light seals (foam or velvet) is probably degraded on the back. Also check how tight the door closes, it may need an adjustment.

The back looked like it was "cleaned" of the old seals. I cleaned them more and installed some velvet light seal material I had laying around. Basically all around the whole back including the hinge and locking area. These were shot yesterday on an overcast day. On a full sunny day ( when I prefer to shoot ) I'll test another roll. Looks good so far.

Nice sunny day shooting sunny 16 ( 1/250th f/11 ) and no signs of light leaks. A very nice camera I'll enjoy shooting. Might add a wide angle lens eventually.