I did another test today.

Loaded the film in dim indoors, advanced the frames to 1, and removed the dark slide. When outside and shot all the frames. During the test, I rotated the back, inserted and removed the slide a few times to simulate typical usage. Condition outside was about two stops brighter than yesterday. I came inside and slid the dark slide in, removed the back, then removed the film.

There WAS a similar light leak but it was well ahead of the frame 1. There was some light piping from the edge but very minor. There was a little more light piping at the end which I assume it happened after the film was taken out of the camera.

So basically, it's good.

Questions to the larger audience....

1) Is this kind of result typical? I am not particularly new to MF. I had M645 Super and Pro before. I don't recall area ahead of frame 1 getting any exposure like this.

2) Above test was basically an ideal condition where I can load and unload film in dim indoor. That won't always happen in the field. Again, I don't recall this kind of problem with M645.