Wow, great progress. There were only a few problem areas left.
There were missing faces, interior faces, and some duplicated faces, which are tricky to find if you don't know what to look for, but I found all of them with that same Solid Inspector plugin.
To make it easy for you, I listed each problem and saved a scene with each one. If you click on the tabs at the top of the screen, each problem is highlighted with a description. If you get lost in the model, which often happens when zoomed in close, you can click the Escape tab to easily get out.
Let me know if you have any more questions!