[K.S.H]

Take it into a body shop and the'll sort it for a while but like others have said its usually too late, might be Ok if its right on the edge. Agree about the preventative treatment, always give them a really good wash when you get them then waxoil everywhere under the car making sure you get well into the corners of wheel arches, I use waxoil and one of them pump action garden sprays, will be doing this task myself very soon, never any rust on my cars but there usually sold before they get to about 6 year old