I'm not sure what makes the difference. I think a lot of it has to do with where they got there gas. I assume that gas stations have filters on pumps? If someone repeatedly went to a place(s) that did not maintain there pumps maybe? I replaced my duster tank because it had a big dent. Both the one I took off and the replacement I got from a yard were nearly spotless inside. I know that is not always the case...
