I designed the spine with an .8mm wall thickness in order to save PLA and decrease print time (not realizing of course it would cause difficulties). I've printed 8 of these that work fine on my Rep2 at 10% infill, .2mm layer height, 2 shells and with the Rep2 standard .4mm nozzle. Does this match your setup?
The spine contains two tubes; auger and marble. I see the gap along the length of your auger tube, however, is the marble tube ok? If so, I can add additional structure down the length of the auger tube.