i'm unclear -- is this picture cropped out of a horizontal frame, or is it a full frame on its edge--turned vertical?

If what you are showing us is the cropped middle of a full horizontal negative then, yeah, your second curtain may be hanging up in the middle of its run. CLA advised.

If this is a full frame, just vertical, then I'd have to ask if the dark band extends through the blank spaces between negatives, because there is no way a camera with a horizontal-running shutter is going to fog a negative like this, if this is a full frame, not just cropped.

scan three negs, with outside border areas, and post that-- makes analysis much easier.

Also, Leica will not service a II. You will have to send it to an independent shop. Essex in New Jersey does a good job.