I have a C&C 25 Mk I. When I hauled out this fall, the rudder drained water, and drained, and drained, and drained. It was enough to raise eyebrows.
There is a hole forward in the crease where the rudder extends forward, and there is the drain hole at the bottom. I noticed at one point that the rudder had become quite heavy, and now realize that the cavity had filled with water.
Fill the hole or not ? Another 25' in our yard has it filled. Any recommendations ?
Austin Scales - Safari - C&C Mk I

I read somewhere that it should be filled before putting it back in the water, and opened up & allowed to drain while dry docked.
Bill Striegel, former C&C 26.

Austin,
On Savannah (25 Mkl) we detected significant water in the rudder. After speaking with former factory service people, I tapped a hole in the bottom of the rudder. The water has an opportunity to enter from thm the gudgeon straps (one of which is below the waterline). Each spring I put the screw in the drain hole, along with some bedding compound, and each fall I remove the screw and let ant water drain out. It is important to let the water drain out so it doesn`t freeze and split the rudder.
John

We had quite a discussion about this on the list 2 years ago . There was a difference of opinion . People with models that do not have holes in their rudder were horrified with the idea of letting water get inside their rudder.
Those of us who have models with the holes deliberitley made by the factory had to ask why they would have put them there if we just blocked them. My 24 rudder has the holes . the first year i filled them but water got in anyway but then couldn't get out and the rudder was very heavy . I got a manual from south shore yachts and the manual said to ensure the holes were open. since then I left them open and everything seems fine. I vote to leave them open.
Ross MacLennan - C&C 24 , Tobermory.

My marine surveyor suggested to drill a hole in the rudder and then install a bronze threaded plug so that at haul-out, you can remove the plug and allow for drainage. I haven't done this yet myself, but maybe the previous owner only got half of the job done. Instead of filling the hole, why not seat a bronze removable plug.
Neil - FoxFire - 1982 C&C32