Optimus Prime (updated, printable)

Nov 18th 2019: UPDATE below original text
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ORIGINAL TEXT:
So here's the thing:

this model is 3d geometry ripped from the videogame "Transformers: Devastation" by me.
The joints are weak, just 3d geometry put together by bones, so maybe they need a few more faces there and there in order to make them stronger (knees and elbows break apart with as much as a hard stare at them).

I've been unable to print it properly, be it ABS or PLA.

Asi you can see from my latest try (first photo), somehow the model "loses" the windshields when imported into S3D.
When in edit mode, S3D shows the complete model. But in preview mode (3rd screenshot), you can see it just leaves a hole instead of treating it as a solid.

Tried importing it into Meshmixer and using the "Make Solid" option. It worked with the windshields, but somehow i lose the face! (4th and 5th screenshots)

I'm uploading it hoping would show up to the challenge and fix this rebellious Prime.
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