To answer your question, the keel is serviceable and you just have to clean it up and paint it. It is the nature of the beast with a cast iron swing keel. Get used to that work as you will periodically have to do it over now and again (or hire a yard to do it for you). The Catalina 22 keel is attached with two bronze hangers that contain a very large SS pin, much like a toilet paper holder (sort of), that the keel swivels on. The bronze hangers are kept in place by SS hex head bolts that screw into a female threaded fixture that is not a nut, but something that Catalina devised themselves. You NEVER use 3M 5200 to bed these hangers because 5200 is an adhesive and there might be times where you need to remove these hangers like in this case: to paint your swing keel. If you like 3M products, use 3M 101 or Life Calks Life Calk, which is a polysulfide caulk for under water use. If you remove the keel, then you can coat the entire keel. If you leave it in the boat, then you can coat everything that is exposed and that isn't so bad either. If you remove the keel, the part that enters the pivot zone will rub off the paint and start rusting eventually anyway. You need to remove the rust on the keel and clean it up. Sandblasting is the best, but you might not have that convenience. Grinding is another solution, with either a grinder disk or a wire disc, etc. For sure get the loosest rust off and if you are unable to clean off all the rust, do as best you can, clean the surface with a solvent and let it dry completely. Like Interlux 202. Interlux also has an epoxy primer that is used on trailers. One is called Rust Lok Steel Primer and the other is called Trailer Coat. Basically the same product. It is very durable and adheres to rusty surfaces well (but make sure it is clean and dry and all flaking rust has been eliminated). Then you can apply several coats of Interlux Interprotect Epoxy PRimer like 2000/2001. There is a window, which varies with temperature, where you can apply bottom paint over the Interprotect without having to sand. Read the label. This should last you for several seasons unless you somehow compromise the surface and start the rusting process all over again.