First of all, amazing asset, thank you so much.
For anybody having problems with missing textures, follow this:
1. Open the .blend file in Blender
2. On the inspector on the right, select Car_Base or any of the car subparts
3. Then click on the "Shading" tab on the top
4. Below you'll see the Material Nodes graph or whatever that's called. Find the left-most orange node that's referencing a texture called '5Car 1_Car 1_mat_Diffuse.png'. This texture does not exist. Click the little folder icon right next to it to choose a new texture, and choose one of the existing colored car textures (e.g. Blue Car Texture.png). This change will propagate for all the other parts. If not, fix all of them individually.
5. Export to your preferred format