Well, we've tried this file for Neck_Joint_Lower.stl in Slic3r versions 0.9.9, 1.1.7 and 1.2.10 (pre-release) and Slic3r appears to work but the foreshortened output file prints a bit of goo and then thinks it's done. Cura couldn't make sense of it either. We think there might be a facet/vertex ordering problem in the source file. In SketchUp it looks like a wireframe with see through surfaces. Any ideas?