OK. I printed half the hull back so I could look at it. The half I printed has printed perfectly BUT there are two spiral vase walls with a gap inbetween. Is that correct? My slicer settings could be wrong, I will double check them;I'm using slic3r. Due to me having a .4mm hotend I had to change a few things but obviously I will try again now.
I did read what you put 4-3mm 120mm long (about 4 times), but my thinking was that it was a typo as the shaft you said was 3mm, so usually you add PTFE tubing outside a shaft and then into brass, so 1mm to PTFE tubing then another 1mm for brass I figured 4mm wouldn't cover all that. Or, I guess you must be using rigid shaft.
Now I've printed I can see it's definitely 4mm. I will probably have to redraw somehow but I'll need to stop running windows10 in VM and do a full install to make this change with 123D; OR I might even try putting a flex shaft inside PTFE directly in what is printed i.e something like this http://www.hobbyking.com/buddy.asp?code=4A18135F-1E17-4D39-85FF-08C5C9BDFFBC, then maybe build a strut for the rigid part out back.
I have that item but will replace PTFE tube with 3mmID 5mm OD PTFE tube and then that inside 5mm ID, 6mm OD brass tube [ (as that's all I could get re: brass tube). So I would have to go from 4mm -> 6mm OR I just try to put that item as it is with 4mm OD PTFE straight into your hole support. If it was solid I think it would work, but it's a thin 2nd layer on my failed print?
Can you confirm if there are two walls or one? in your print?