Vegasdan you must be talking about something else and not extend. Yes you want to get rid of any oil. I don't know much that will stick to oil. Then all you do is get rid off loose rust (wire brush) and apply two light coats. You do not have to top coat, if you are not going to top coat you add a third coat after 24 hours. Don't know what you are talking about the finger prints, never read anything about that. The surface needs to be rusted to get the chemical reaction for Extend to work.
Sunny South Carolina
2004 Pace Arrow 37-C WH W-22