I use WD 40 and a rag to wipe off the excess. It actually will remove some of the rust you already have as well as prevent new rust.
Actually this is what I'm doing. I just wonder if I'm only removing the outer surface rust. Just wondering if there was any product that would penetrate the wire twists and neutralize the rust that I'm sure is working between the wires.
The only methods to remove rust between twists that I know of involve acid or the removal of some of the wire, electrically. Neither seem like a great idea on standing rigging.
Wash and soak the rigging throughly in fresh water to remove the salt. You can use paste wax to remove the rust stains. The wax will provide some protection and will not collect sand.
Be very careful about who you tell that you wax your rigging. The only people that I know of that wax their rigging, also scrub the black parkig lot marks off their black Cat Trac tires.
