What we do to extend the life os stainless for coal is right when people shut down for the season we clean it and spray it down with wd-40. But really clay is a better liner for coal
How the heck do you spray down a liner with WD-40? I picture a pump spray can with a long hose attached getting dropped down the flue. Then you have to twirl around the spray head 360 degrees on the way down. Sounds awkward.