Odd A12 experience.

[Anscojohn]

I have an old-style A12 back which has just begun fogging on the right (inside), and overlapping about 3/4 frame through on a couple of rolls. I'm pretty sure I know the cause--that plastic thing in the mag that mates with the body drive gear is probably worn down, and I need an overhaul. Actually, the mag needs an overhaul is what I mean, although I could use a few new parts meself, come to think of it.
Howemsoever, when I loaded a roll, went to frame 1 and set the counter, then rolled past to frame three, the problem did not happen. Last roll I did the same thing, only with one blank frame. Everything was fine.
Anyone else have an experience like this?

 

[bdial]

Sounds like you actually mean a manual back, the kind with the window?
In any case, I have an automatic back which overlaps the first two frames by about 1/8 inch once in 20 or 30 rolls. It's due for a CLA, but I'm not eager to spend the money quite yet.
What happens if you roll a bit past frame one, then set the counter?

 

[John Koehrer]

Besides wear, the nylon stop could be sticking a bit. The stop is, by the way is in the body not the back.
If it's the stop it should happen with all of your backs. Even if it's intermittent.

Want to take the body apart? It's very simple & the stop is right there in front of you.

 

[Q.G.]

The nylon stop is in the magazine, John K.
But is not the thing that mates with the gear sticking out of the body A John.

Either of two things (sometimes both) will be responsible for most framing issues.
First is that nylon stop. Over time, it gets a considerable beating and gets dented. And that will cause frames to overlap on the entire film.
Second is the adjustment of the counter mechanism. That causes overlap of the first two frames.

But a combination of either or both, and/or other things (wear of other parts, loose screws, bits of the mechanism sticking etc.) can cause havoc too.
The best thing to do is (no surprise) to have the magazine cleaned and adjusted, and the nylon stop replaced.

The light leak is another thing. A thing i can't give relate to the frame spacing thingy yet (maybe the gears didn't mesh properly, with the camera's gear kicking the back away from the body far enough to let some light in. And that out-of-synch meshing could also be responsible for the spacing issue?)
Where exactly is the leak, and what does it look like? Can you show an example?