Hope you are well,
Still stuck with this? Looks like nobody kicked-in so far, so I quickly had another look this morning. Sadly with no real success/answer, I have to admit 
May be this post could help you. It has a slightly different approach but might become an alternative if the solution does not come.
Sadly, we lost johnK a few months ago. A great loss for our Community and then of course, for his family and friends. I’m sure he would have had some interesting input on this.
Else, I believe there’s still another way to create a torus/donut shape like extrusion. In fact, it’s the solution I would have picked although there’s indeed a downside to it. I would create an extrusion of a circle with incurvation on a complete revolution. The downside being that where it connects it would still have a noticeable start/end. It can be lowered quite a bit working the texture, but since it doesn’t just close (only connect), I guess it will always remain noticeable.
Let’s just hope the weekend will bring new people to try solve your issue. Meanwhile, have a great weekend (anyways) 