[Silent Street]

[...] and a clear light leak peering out of the middle right side. There were some frames in the rolls which did not show this anomaly, but a majority had the issue.[...]

That part is definitely light piping caused by careless loading/unloading, as iterated in an earlier post.
Re light seals: Seals very rarely give any problems with either the 1960s era Pentax 6x7 or the 1989-issue Pentax 67. More people experiencing light spoilage from roll inserts/removals than any other factor — and blame the camera! If there are seals on either Pentax that require attention after a while, by and by it is the seal around the TTL/non-metered prism. Neglect of this can result in the prism coming off of its own accord.

The shutter curtain is rubberised and pinholes are exceedingly rare. A more common malaise is cigarette ash being blown onto the curtain and scorching it. Replacement is from another, cannibalised body, so you are essentially replacing one old component for another, potentially less reliable piece. That is the way it is with the old Pentax MF cameras.

If you are concerned about any anomaly in the processing (such as the banding), take the entire roll back and point out the problem and ask for a refund of your money. The roll does not appear that any of the shots on it cannot be repeated at will.

[wombat2go]

Hi Addison,
Looking at your post #3 neg of Portra 400, I wonder if that is a coating problem during the manufacture.

For your post #12 about removing bands, I can comment that I have used the parametric selection tools in Darktable,
in the "soften" gizmo.
Parametric selection allows a change confined to a range of RGB or, ( better maybe) HSL.
That allows us to, for example, reduce banding only in ranges of the blue sky, while leaving the main areas unchanged.

Here is a photo on home processed Fuji 160 , camera RB67, 50mm lens, scanned by the PrimeFilm 120Pro,
after correction using parametric selection, to reduce some banding artifacts in the sky:
https://app.box.com/s/qlyxwm9skjvkd8dtalbu50oavfp6vi8s