I just thought I would put a post out there on something I just learned about Windows 10 ( Sorry Mac users). Windows 10 comes with 3d printing software called 3D Builder, I used to repair files that were not manifold with Netfabb, but with Windows 10 3D builder, you just load your stl into the software, and click on the check mark to continue, and if it is not manifold it will say, One or more objects are invalidly defined. click here to repair, then just click on the message to repair the model. then save your model, there are four different save formats, 3mf, stl, obj, ply. I am sure the software does more, but I just found out about the repair function and thought I would Share the info.