I tried using the Mac version of Rhino for object creation and had a lot problems with the meshes created. Many of the surfaces were flipped, there were open polygons and boolean operations were prone to have unattached polygons. If you can reveal the triangulations of the polygons look for points that appear on one polygon but don't have matching points on it's neighbor. If you grab the point a move it a bit and it leaves a hole on what should be a solid surface then that is what I was experiencing. You may wish to download and use MeshMixer to evaluate the files exported from Rhino, I eventually gave up and brought the meshes into Cinema 4D for cleanup and rebuilding as necessary. Now it's my primary application for modeling items I intend to print.