Some textures won't cooperate

Hello everyone.
I am currently working on a porting from Train Simulator 12, but every time I spawn the model in Gmod some parts are with the wrong textures…

Here’s a screenshot of how the model looks like in Blender and should look like in Gmod:

And here’s how it looks like in game:

I have to note that the person who made the original model made a HUGE mess with the materials, so I had to rearrange all of them by myself. I tried everything but I can’t understand what’s wrong with the front part and the pistons… Could anybody help me please?

Here’s a link with all the files if someone needs them: https://mega.nz/#!7BZjyBqL!EAUh6vMHOO7bbQlEXF5z88NCvP43LgcHS6CcSipIaos

Thanks in advance.
**
EDIT:** problem solved, I made a mistake while applying a material.