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.
I’m going to try rotating the profile in the blue axis to be normal to the arc, then extruding.
Rotating the profile normal to the arc did it. I can live with that.