Thank you all for your replies. It's been some time since I updated, I wasn't able to work much. But I'm slowly making progress. I realised that my diffuse looked flat, so I'll try a different approach: instead of a metal texture, the vent will have a flat color (with a minimal grunge), I'll paint in the larger scratches…
Started working on the diffuse texture, it's still a very early wip, but I'll post it, so that you can get the basic idea of the texture. There's still a lot to do, I'll post some updates soon.
Sorry for the delay; I finally had some time to work on the maps. I improved the diffuse and started the specular. It's not final, I'll probably work on the scratches on the specular a bit more. Anyway, here's how it looks right now:
Quick update on the textue, I'm not finished yet; I'll paint some scratces in, overlay a grunge texture and refine the red stripe and the rust on it. If you have any other suggestions, feel free to post them. And here's the diffuse, it's 1024*1024, but I'll resize it; as I know a 512*512 map is enough for a prop like this.