Hi Burr, I have attached a tuned up version here as redo2.zip .

I think it was the one curve piece for the donut part sticking down a bit too much which kind of instigated the misalignment. It seemed to be sticking down further more on one end than the other.

To tune it up, I turned on control points and used Transform/Align to make sure all the bottom points were all lined up on that base axis line.

Then I built the longer sweep part, and the donut sweep part, then selected them both and used Edit/Trim to cut them with each other. Then Edit/Join to glue them together.

That results in the surface in the file there which I slid a bit over to the side from the curve framework.

This piece now has a planar opening on the bottom, so you can turn it into a solid by selecting it and then running Construct/Planar - that will seal off the open bottom and you will have your half-solid piece already there without actually doing any boolean.

Then if you want to make a matching bottom solid half, you can use Mirror on that and you will have your bottom solid piece.

I hope this helps, and please let me know if you need any more info on the above steps, and thanks to Danny for zeroing on the problem!

- Michael