An idea is to use Tamiya X19 Smoke to seal the steel. It will give a nice glossy finish and in the mean time it will look like a light worn cuirass. Usually, I used X19 after the oil washes dried. This for heavy worn cuirass or armour, but in your case, maybe you don't wont to present him like that. That's why I suggested to use X19 only. It's worth trying. You always can go to inks or oil paints after you applied the X19 if you don't like how it looks.
Looks awesome, so far.
Cheers,
Zeno