Local garage in Marion, Ohio known as(incidentally) The Muffler House.
I know the last time was from the cat. on back, I think time before that was just the muffler, I don’t quite remember. I think they just use regular metal each time, stainless steel is optional IIRC. I also consider it part of routine maintenance due to my driving habits(less than 7 miles one way to work, about the same distance to the store with random shorter trips and very few long highway trips), and salt on the roads.