So sorry to hear this! Long post coming - sorry all....
I have not yet to do any serious rudder repair on a 323, so I am not sure what is inside. However, if you trawl the web you can find sites like this
http://mysite.verizon.net/~vze339xh/steve/boatpicspage.html or
http://www.kp44.org/rudders/rebuilding_rudder.php that show possibly similar work. Note that the internal structure of a rudder is generally stainless steel rods welded to the rudder stock, with a fiberglass "shell" over it to give the rudder its shape, and some kind of filler (e.g plywood/foam). If the interior of the rudder has become saturated, it is not uncommon for the weld to break, and the rudder therefore to fail. The most common definitive repair is to remove the rudder, split it in half, fix what needs to be fixed, then reassemble. Hopefully in your case it will not come to that.
Now on to what little I do know ;-). When I bought Selene, when she was on the hard awaiting a bottom job I noticed a very minor drip - teaspoon a day - from the stern of the keel. Interestingly the surveyor said that a reading taken in this area is meaningless as the copper in the antifouling prevents moisture meters from getting a reliable reading. So he just tapped a lot...said it did not seem too bad...
I drilled it out - still weeping a week later. To make a long story short, I ended up grinding off the a bigger and bigger layer of "skin" on the port side, ending up perhaps 4' square exposed, (in the stern - the false keel). What we have is a layer of fiberglass from the mold, filled what appears to be some kind of poorly-poured low-density epoxy (maybe the rudder is like the false keel?). Mine ended up like swiss cheese; holes and pockets everywhere, filled which whatever bizarre chemistry was available - different colors of the epoxy showing earlier attempts to repair -I hit pockets of oil(!?), acid, water, milky stuff, air...anyway a vacuum pump dried it out as much as it could, then we refilled. The attached photo was taken just after I started...the final exposed area was a lot larger.
One observation was that during construction the fiberglass roving in the keel may not have been fully saturated - or seawater is even more corrosive than I thought! As I started grinding way, the top layer almost peeled off and the fiberglass was rotted for ~1 foot on either side of the original leak; a layer of black mush, ~1/16", with a few fibers, sandwiched between the Gorgonzola-like filling and the thin outer layer.
Anyway - too long a ramble - my big worry was that the rotten fiberglass had reached the encapsulated lead keel. If the glass/epoxy/filler around the keel becomes saturated, that can be a real problem, as the keel can break free within its encapsulation, providing an ideal place for water to wick in around the keel and soften the entire structure, so the keel ends up encapsulated in black mush (shudder) - a problem which is very expensive to repair.
In your place I would do some investigating (grinding) in the suspicious areas - maybe cut an "inspection hole", take a core sample from the rudder. As I am sure you know. fiberglass is very forgiving - an exposed area can be dried out and repaired to the strength of the original. Also, you also may want to consider when to do this, as an extended period on the hard is quite possible.
Good luck!!!