Before I printed the test above, I ran a test to fine tune my retraction & extra restart distance. I set up a 3 by three grid of models, varying the parameters up & down slightly. To do a fast check, I only print the lower 5 mm of the models, which results in a 2.4 mm thick ring. With a 0.41 to 0.42 mm actual extrusion width and telling the printer it's 0.4 mm, there should be NO gaps, without any need for fancy extrusion width adjustments or gap fill.
Here is a photo of the model that came out the best:
I still have gaps.
I stripped the S3D file down to just this model & process settings, and here is the factory file for that:
There have been lots of reports of this issue going back years, including more than just this one from me. Some users have reported testing their models with other slicers, and they don't have this problem. If nobody can spot a bad setting in my process, I will have to try to print the part in PrusaSlicer. I'm no where near as comfortable with PS as I am with S3D, but if they don't come out with an update of some sort that fixes this, I may have no choice.