Ok, first off... here are all of the minor issues:
1. You're using a lot of double-sided polygons. I should warn you that these often render a bit funny in Spring, when any reflectivity is enabled, and I usually avoid them, even at the cost of slightly higher polycount. However, that's a minor issue.
2. The orientation of the model was wrong, it was turned sideways. Again, super-easy fix. See upper-right window for the way the front of the model should be facing.
3. You needed to do Object-->Recalculate Normals, then follow up with Object-->Recalculate Vertex Normals, 3DO-Style (all objects), to get the shading right and correct the smoothing. I used an angle of 45 degrees, it worked for everything, as even the round "radar dome" will look rounded with that smoothing angle (anything less than 45 degrees is smoothed, when that's the number you give UpSpring).
That will fix the blackness, if it's cause by welding problems, or, heaven forbid, bad vertices- it won't fix bad verts, but you'll see them.
Now, to see a good preview, you need to use the following viewport settings:
That will show you if you're having serious problems due to welding- although it's not exactly like Spring's renderer, it's very close.
The biggest single issue, though, was that you didn't define a texture2. The texture2 is used for the glow / reflect map, and 1-bit transparency. It's not optional. I've posted the one I use as my stock file, along with a shrunken 8:8:8:8 DDS texture (more or less lossless) of your main skin, which looks practically identical to your 1024 skin at a quarter of the size. Don't use TGA, they're huge, require Spring to make the mipmaps when the Unit's built, and the textures have to be upside down- UpSpring renders them right, but Spring doesn't, for some unknown reason. I'm sure that certain people around here will say otherwise, but tbh I think that 8:8:8:8 DDS is the way to go- lossless, but without the problems of TGA.
Click here to get the updated MG Rex. Let me know if you're still having problems, that should have sorted it out, though.
[EDIT] The model wasn't centered on the X axis, either... fixed...[/EDIT]