Quite a nice result Michael, viewing the standard size on AstroBin it looks pretty good, some processing artefacts, wonky stars and column defects are really only noticeable when viewing at full size. The resolution around the keyhole is pretty good
Yes dithering more may help I guess..? Or in Astroart6, that I use, there is a column remover available in preprocessing, you just identify the column and it will be removed in every sub as part of calibration.
Mike