Hello again Ian......
I do move my vise grip or C-clamp connection point at least once during the cleaning process. Not only does this allow me to re-position the iron a little, but like you noted, it does allow the spot under the clamp to be cleaned like the rest of the iron piece. The C-clamps that I use are not plated, and if they were painted, I scrape some of the paint off for a good connection for the vise grip. The vise grips are plated, probably chrome??, and they do not turn black. They do get a coating of brown discoloration, probably from the solution, but most of it washes off with soap and water. As for the "S" hook idea.... I usually clean off a spot on the iron, if it is really crusty, so that I have a good contact area for my clamp. You are doing the same thing with your contact point for the "S" hook, the only difference being is that your iron is just hanging on the hook...still a loose connection, IMHO. Did I mention I like tight connections...lol. I think I have also seen someone's set up where they used a short length of chromed chain....it may work, but IMHO, still just more loose connections. The fewer contact points and the tighter the connection, the better off you will be. Keep playing around with your set-up and have fun experimenting.
Scott