Question for those experienced with metal. A few months ago I cleaned my exhaust pipes and lightly polished them by hand to get a nice satin finish (first pic). Recently, I noticed that the section of midpipe closest to the rear header has what looks like pitting (second pic). However, when I run my fingers over that section the surface feels smooth. What is this? Is this normal and if it's not is it repairable? If so how?
