I solved it by importing the OBJ into Hexagon.( still availble free I think?
) On import you get an option to weld any disconnected verts occupying the same space ...something like that...was a while ago! I reckon that is your problem, you just need to make sure all your vertices are welded.
Heck, it even has a rudimentary cloth simulation and instancing!
It is completely possible to finish a complete modelling project without ever having to leave the application.
3DCoat uses both polys and "Voxels" volumetric pixels.
I have been big fan of 3D-Coat since version 3; what caught my attention that time was the ability to unwrap models so easily and per-pixel painting.
I didn’t dare to step into the sculpting room since I was such a big fan of ZBrush since the earlier days and didn’t want to compromise my learned shortcuts.
The present version rivals and even surpasses some of the features in ZBrush 4R7, and now after 4.5 update 3D-Coat can do PBR.
(Only thing ZBrush can do at the moment is a BPR, a Best Preview Render, not PBR, acronym chaos! It can do both volumetric and surface based 3D sculpting, re-topology, UV unwrapping, per-pixel texture painting directly on a model (without never having to watch UV seam), baking, PBR in both variants (Metal-Rough & Spec-Gloss), Ptex, and render nice previews of the model with HDRI environment maps.