Upright Extruder produces end profile slightly out of plane

Thanks to Dave, I know about the Eneroth Upright Extruder used in combination with the Dave Method. The attached file is already scaled up 1000x.

Extruding the profile below along an arc I expect the profile at both ends of the extrusion to be aligned with the coordinate axes so that the resulting extrusion sits “flat” against a plane described by the Red-Blue axes. In attempt #1 the UE stops just short of bringing the end profile into the plane. In attempt #2, I added 10º to the original arc and extruded again,. Then I subtracted using a rectangular solid to get both profile ends “flat”. The resulting end is slightly twisted. Any idea what I am doing wrong?

Wireframe showing desired position of curve and profiles.

Essentially, the curve is inscribed on the inside of a cylinder.

Bare curve with profile to be extruded.

Attempt # 1 with line in Red axis illustrating the unexpected end profile alignment

Attempt # 2 extruding through an additional 10º, then trimmed flat using a rectangular solid with solid tools ‘Subtract’. With line in Red axis illustrating the “twist” present in the end profile.ComponentDrawingFile.skp (7.7 MB)

Thank you,
Ted S

What is this thing and how would it be made in reality?

Prototype 3D printing. Production injection moulded fingers crossed. Resin to be determined. The slots hold gaskets.
[Edit]
I’m going to try rotating the profile in the blue axis to be normal to the arc, then extruding.
[Edit]
Rotating the profile normal to the arc did it. I can live with that.