You will be fine man. That is common for metal parts that get a ton of heat soak. The VIII exhaust manifold cover did this immediately, and it never showed any signs of rusting through.
You think because of running to rich and unburn fuel. My baby brother was following me in his NSX. His car sits fairly low, we were passing by a hilly area with alot of small up and downs. This was when he said he saw the brown look like rust in back. I dont know, it just looks bad now that i notice it.but not like it will matter to me since im going with buchar racing soon.
I think I'm more concern about the way it look, You notice it alot more because the can is sitting side way.
Its just looks real bad, driving around a brand new car and you can see a big rusty can. My VIII and 9 both has it to
but it never happen this fast, But you can't really see it because the muffler sits the normal way on the Older EVO.