There may be a build-up of muck around the inner wheel arch lip. Remove any plastic liners and clean it back.
With abrasive, remove all existing coatings.
Remove pitted corrosion with Deox-Gel. This may need repeat application and make sure work is carried out over 10 degrees C as it will be too cold to work otherwise.
Prime the cleaned back steel with Electrox then topcoat to finish.