This a 15 image stack in DSS. It shows Comet C/2012 F6 Lemmon, 47 Tuc, and the Small Magellanic Cloud. It also shows severe streaking generated in DSS for which I can find no cure. It was shot on a Pentax *ist DS and a standard 18-55mm, all on a tripod. Exposure would have been 30secs @ISO 3200. I am fairly sure that I included darks in the stack. Any comments would be appreciated.

Have you checked each of the 15 images to see if they are ok?
You could try Sequator: Download - Sequator and see if it changes anything.

It almost looks like you had some trees in the bottom of the frame there. Apart from that the other streaks you see are what I got when I stack my comet picture of 46P/Wirtanen. If I pull up the brightness I see the same streaks in the star field that you have but not the streaks at the bottom that I'm guessing are trees.

If I am right DSS first stacks on the comet, then subtracts the comet from every sub and stacks those subs on the stars for the final image and adds the comet image from step one. If only a few images are in the stack the median function in the first step will not eliminate the star trails completely. This often leads to streaks in the final image and was the reason why I have tinkered my image of C/2019 Y4 (Atlas) "manualy" in PI and PS.

What is not explained by this is the length of the streaks (and of the shift in the trees) that can not result from 7.5 minutes exposure time with an 18-55 mm lens.