I'm pretty good at problem solving these things and have solved many camera issues and have repaired nearly every camera problem I've had in the last 15 years, but I'm stumped here. I feel like it's one of those "looking for the ketchup in the fridge and can't find it, because it's so infront of you, you overlook it" scenarios. So, here's the facts, followed by some pictures:

- The camera is a Leica M4-P
- The leak is consistently in the same spot in about 25% of the photographs, but it varies in intensity. It spreads vertically, up and down, 8mm from the edge of the film.
- The leak never goes outside the frame. In some instances it would stop right at the edge with no leak.
- The leak has not pattern between frames. It might hit 3 in a row and then none for 10.
- It's worst on sunny days.
- Last week I shot a "sharpness test" roll with the camera on an overcast day. One subject was a brick wall, 10 feet away, the other subject was a landscape. NO light leaks occurred during this test roll.
- Upon further inspection of the "nature" of when these leaks show up, they happen mostly between shots where a lot of time lapses between them. When I shoot 5 frames quickly, there's never leaks between those shots.
- The brightness of the leak is nearly the same intensity all the time, just spread over a bit more. I can burn it in for the most part when printing in the darkroom. I've seen light leaks that KILL the image and make it completely white. This one just changes the density slightly.

So, my logic was to test the curtains for a pinhole (doesn't leak out of the frame, always in the same spot, bright days show the leak while overcast days don't, is more intense between photos where I do more walking, etc.). I couldn't find one with a light in a darkroom.
Thought it might be the curtain dragging on a burr on the track, but after 523048 rewinds, I couldn't see any drag.
Thought it might be a screw on the outside of the body (there's 5 of them). One keeps turning and turning that leads into the take-up spool. I thought it might be that, but given that the leak is ALWAYS 8mm from the edge, it doesn't make sense that it's from the body - otherwise as the film layers increase in the take-up spool, this measurement would change.
It also cannot be on the camera body on other spots or else it would leak onto the edge of the film.

So, I'm at a loss. Is it possible that there's extra wear in the curtain that I can't see with my human eye, but over time it while the shutter is chocked (and waiting for the next shot), it's slowly leaking?

At a loss. Any help would be great. Thanks in advance.