Steel wool will scratch chrome, it doesn't matter if it's 0000 or not.
This could be the problem the original post is asking about... If you are really going to town with a lot of pressure you can be dulling the chrome.
It may look really good when you have some dull chrome next to rust, your thinking this is working great. Than you put your freshly scrubbed chrome up against nice original chrome and it doesn't look so shiny anymore... Brass is the way to go. All of the big box stores sell brass brushes near their welding stuff but they are expensive. I usually find them cheap at Tractor Supply, Big Lots, Dollar Tree, Etc.