I know someone asked this question and I read all of the answers but I guess I am still not satisfied. I saw the suggestion was given to get textures of scratches and bumps from a site that is good at making hi res textures. However, I am wondering if that is what you did for the texture here? Can you UV unwrap and then send it into photoshop to make it all black and do white scratches across the sections you want them on? This way you more control the grudge look you are wanting and make it specific to your model. I know you can make normal maps and bump maps in photoshop.
There's several ways you can create a bump map. For this roborb model I used photo textures of grimy scratchy metal. The reason I choose this most of this time is convenience. We could paint anything by hand, but you have to be good at hand-painting and you have to be patient during that painting process. At least compared to simply loading a photo of the texture that mostly fits what you're after.
But yes, you can easily lay out UV's in Blender, take a UV snapshot image, open that image in Photoshop and paint a custom scratch/grime texture. That's a fairly old-school way of texture painting but it's still plenty viable. You can also paint directly on your model in Blender.