Having some basic knowledge of metallurgy, I can't imagine how soaking cold metal in Diesel fuel would do anything but get it wet with Diesel fuel...
The cables are galvanized. No point it putting a "protectant" on them. that just makes them slippery when handling.
Just like Synthetic rope, cables need to be replaced every couple of years if they are used often. fraying, stretching, nicks, and kinks all allow for rust to get into the cables and weaken them.