Hello John,
Wind causes a different effect, where this is a clear elongation in one direction. It could be another issue, but when a separate guide scope is used, the issue will often be flexure.
At this focal length, even a fraction of flex in one element will have this effect on your image. Your polar alignment and guiding can be perfect, the result will be the same.
Wider fields of view suffer less from this issue. Resolving the problem is not easy, but there are many sources on the net on how to proceed, but, it’s up to you what to do and it just depends on how much it bothers you.
Like I felt, your image is very good.
Cheers,
Steve