Welcome to Sailnut FishDragon.
Good for you for getting your boat the he!! away from the storm surge of Sandy!
Here is the spec of the Mac 21': MACGREGOR 21 sailboat specifications and details on sailboatdata.com
I'm not very familiar with the V21 so please bear with me.
As Faster suggested, if you can actually remove the rudder when you are not using the boat it will not get nearly as many barnacles. This is a great idea, especially if you end up using sub optimal marine finishes on the surfaces. Varnish, most finishes and most paints will not last too long when submerged in water for a long time, especially over a wood surface.
For your metal surfaces/plates I'd think about using something like: Pettit Zinc Coat Barnacle Barrier
The problem with wood in underwater use is that it will swell, eventually causing seams that allow more water intrusion. The most widely recommended course of action would be to clean/sand down to wood and coat it with epoxy and glass cloth and then apply an anti fouling paint of some kind. If you can keep the rudder out of the water most of the time then a good marine varnish, with 8 - 10 coats could certainly last a season (perhaps 2 or 3).
Not that I could not understand your post (pics help a ton BTW) but the 'nautical' terminology for the pins on the rudder are 'pintles', and the female opening they fit into on the transom, or back of boat, are called 'gudgeons'. That should help if you want to find new hardware as it seems to have a patina of rust and is likely stainless steel (SS), which can/will fail.
I've had rudder failures before in boats smaller than your V21 and it never seems to happen when it does not matter; it is always when you need it most.
There are ways of actually steering a boat without a rudder but it is not something you want to learn quickly in an emergency. It is good practice to be able to come about and jibe without a rudder though. I've done it in smaller boats but should try it myself on my 27 footer.