Hi JM, can you please also post your original 3DM model file in it?

It will probably be easier to look for issues in your original model file rather than only examining the STL triangulated output.

One of the main tools to investigate holes in a model is to set up a shortcut that will highlight naked edges (edges in the model that only belong to one surface rather than being joined between 2 surfaces), which is described here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6051.2

When you select an object, if the object type indicator in the upper right corner of the screen says only "Surface" or "Joined srf" instead of reading "Solid" it means you have some naked edges somewhere in the model, which is preventing the model from being a watertight solid. The naked edge script can help to show you where those are at. Then you usually need to build some surfaces and join those in to make it a complete solid.

It can also be easier to try and keep your objects as solids from an earlier stage in modeling rather than only building things in separate surfaces, but for some shapes doing it at a surface level can be useful too, but you need to keep track of what areas are not finished.


- Michael