As I have written before, coating an exhaust pipe with oil will eliminate
rusting.  The oil has to be applied while the pipe is warm, not hot, preferably
as it cools down after running the car.  The guy who turned me on to this
sprayed used hydraulic oil on the headers of his sprint car, but, after seeing the
rust-free cast iron pot I use for deep frying, I now recommend peanut oil.
The more applications, the better.  After a while a deep bronze impenetrable
coating will become one with the pipe.  The most fastidious Vanagon owner I know,
The Tube Guru, has tested this on his own jewel and is now a practicing
member of the cult.  The neat freak that he is, The Tube Guru prefers to use a
brush to apply the oil.

George