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The biggest problem regarding rust is the tough to find spaces...inside the tubes and at the junctions. I use old congealed oil, these's always a bunch around and coat the inside of the pipes every time they are off. Once every few years I guess. Then the heating smokes them a bit, but it bakes on a layer. Outside clean is best, but I let a little oil bake into the spots I have trouble reaching. Perhaps this is my round engine backround talking...