Hi Beetle, I've attached an edited version here which should now boolean difference ok - the change I made was to go to the front view and slightly stretch the cutting tubes in the z direction using the edit frame, to avoid that situation at the bottom with partially overlapping pieces at shallow angles to one another.

- Michael

Also I noticed that the planar end cap surfaces on the cutting tubes is a generic "cubic" surface rather than an analytic plane surface, that may have happened as the result of a deformation command, when doing a Transform > Deform > Twist or Flow, the entire model structure gets converted from any "analytic" exact sphere, cylinder, or plane type specialty surfaces into generic squishy surfaces. Having analytic planes can help for booleans rather than surfaces that are just a general surface but that happens to be shaped as a plane. So in a case like this it could help to delete those end caps and reform them by selecting the surfaces and running Construct > Planar which will then put new analytic plane end caps on them.

I've made a note to myself to look into automatically reforming end caps like that to be analytic planes after doing a deformation transform.

But the easiest method is to make the cutting objects continue for a little ways past the end of the base object rather than having them stop right in the same spot.

- Michael