Wire brush the threads first, or soak/clean with toothbrush (see above). After drying thoroughly, you can optionally put a dab of white lithium grease in each swivel nut, install tension rods, and wipe off any excess grease with a Q-tip.
If you have a bar clamp wide enough, squeeze the shell perpendicular from the split to open it wide enough to fill with glue. Flexible glue (e.g. tacky craft glue) is better than hard glue (e.g. Titebond). Most glue can be thinned with water to be sure it flows into the crack. After glue is applied, release the clamp & squeeze the area tightly. It helps to have something pliable between the shell and clamp like cardboard or layers of veneer glued together to distribute the pressure evenly.
Soak chrome-plated parts in a bath of citric acid powder (3/4 cup) and water (1 gallon). Rub with aluminum foil, Scotch Brite pad, or toothbrush to remove rust and filth. Then use Nevrdull or chrome polish to finish.
Don’t use steel wool as it can scratch and dull the final finish. White vinegar can be used to soak mounting screws and washers. I have heard of people using the blue Dawn (dish soap) instead of acid, but I have not tried it yet.