Weird problem with subtract/cut Boolean tool using fusions

[residentegg]

FreeCAD 0.20 on Windows 10 machine

I'm attempting to subtract a fusion of torus and cylinders from an exact copy of the same fusion only using a different diameter for the torus and cylinders - basically: trying to make a pipe. I know the Design workbench allows you to do something like this with a sketch and using it as a path to extrude along. I have not been able to make that work since I can't wrap my head around using the constraints system on FreeCAD yet. Regardless of that... I have been getting along fine using primitives up until now. For some reason when attempting to subtract "Fusion 37" from the "Exhaust" or "Exhaust (Solid)", it subtracts the entire back half of it. I've deconstructed all the way back to "Fusion 33" and "Fusion 33 (Mirror #14)" when expanding into the individual parts of "Fusion 37" and those seem to be the problem parts. Copying them and attempting to create a union between the two parts ends up "deleting" the other. Is there a problem with how I built that part and its mirror that I'm missing?

Thanks in advance.

Google Drive link to FCStd file

[chrisb]

Hi and welcome to the forum!

Part > GeometryCheck shows an error on Exhaust. After such errors it is often the case that subsequent boolean ooperations fail.

[Shalmeneser]

Your file without the car.