So yesterday I tried out a rusty look on a marine. He is one of the marines I made for fun.
Heavy bolter with a little conversion on the weapon. A dragonhead from the chaos vehicle upgrade sprue. This would be the look I would go for my Sanguairy Guard, Priests and Dante.
About the helmet eyes I'm not so sure.
I followed the rusted part metal from the tutorial made by Kaptirowski. Which he used on his Death Guard. Tutorial can be found here.