Hi Ed, other than using slightly different tubes, it is possible to get it done with equal sized tubes but it is a rather difficult to describe process of doing more "low level" surface trimming.

I've attached a result file here for you to use.

To make it, I started by deleting the control point at the juncture between each segment of your sweep path, to fuse those segments together into a single long segment. That makes a more simple sweep result since it will be one single surface.

Then I did a boolean to cut that single tube out of the base ring. Then I started with the surface modeling techniques - I separating things into individual surfaces, mirrored the channel surface, did some manual Trimming with the outer ring surface and the mirrored channel so that the outside piece was cut properly, then there was some cleanup work doing trimming of the 2 channel pieces with one another. I used "ShrinkTrimmedSrf" on the pieces so that their underlying surfaces were not closed surfaces, which seems like it may help to avoid the problem area in the intersector. After all of that trimming then I joined the fragments together.

It's a rather complex process so kind of difficult to describe well, but the result is attached for you at any rate.

- Michael