I've done a bit of digging but can't find any post on exactly this topic. My bowden tube, normally locked in place in the extruder mech via cutaway slots in the plywood mount and the locknut plastic screw fitting, has broken through those locators and free of the extruder assembly completely, stopping extrusion.
I think the cause of this problem was increasing the flow too much, in error.
See attached photos. This breakage is very disappointing. Is there an improved extruder assembly I should use instead? Probably I will just epoxy the fitting back in its location, which will do for now. It would have been better if the unit failed in some other more reparable way to this issue of too much 'flow'. Thoughts and comments appreciated.