Here are some photos from Tim on KP44 Canopus, showing crevice corrosion on his rudder shaft.  Tim's comments:

"Not much was visible on the pintle until I whittled it away and finally opened-up the rudder.  The rudder is well made and although the edge join was not particularly good everywhere, there was little evidence of water intrusion.  Also shown is how the shaft/pintle are welded to the plates in the blade.  A local marine fabricator is making up new parts in 316 and welding them up before I re-glass that area. You cannot see this problem without taking the rudder off!!"

Also see the article by Rick Crane on Removing the Rudder on his KP44.  For information on crevice corrosion see Corrosion Problems Associated With Stainless Steel.  Greg Rodgers on KP44 Second Sally has detailed their approach to fixing rudder corrosion in his article Rebuilding The Rudder.  Britt Finley on KP44 Restless describes coping with rudder loss underway and repairing his rudder in Fiji in the article Rudder Failure and Rebuild.