Hi Jim, I've got a 'new to me' 2009 C375 that had a rudder void and wet area that was surveyed when we bought her last fall.  We had the rudder dropped and professionally repaired as part of the purchase, but checking out the reinstallation, I was surprised at the room and access to the rudder tube and steering- the top bearing and retaining ring are secured by bolts, at the top of the tube.  

If you climb into that huge aft port lazarette, you'll be able to see all of it.   There's a decent diagram on the Catalina Direct parts site, look at the replacement bearings page :  https://www.catalinadirect.com/shop-by-boat/catalina-350/hull-deck/stern/rudders/rudder-bearing-c-309-c-310-c-350-c-355-c-375-c-380-c-387-c-400-c-42-c-445/
 

Tom