Army Aviation;
Generally the rudders are two halves with either a wood or foam core married together with marine putty and then covered with fiberglass. It is obvious over the years that due to wear and tear and who knows what ever, that you have issues. Good advice given but as a servicing dealer who repaired many over the years, the first is to let it dry out which you advised it did but to many let the rudder stand up with a hole for moisture or water to escape in a dry place out of the sun. Not knowing what you exactly have, I would remove all the old paint or coating that is on it wearing masks outside with a cover on the ground or using a dust collector style sander such as a palm sander with filter attached down to the gel coat. At that point I would apply a two part epoxy to fill in the holes and depressions. I use to buy Watertite by Interlux and yes it is expensive but sure does last but most important is a slow cure and to be blunt the hardest and long lasting. Then spray light with some paint over any major voids if large and then wet sand to see if there are any valleys left that will need a second coat. Then you will need to build up the fiberglass as suggested on the leading and bottom edge of the rudder. You will probably will not be able to do this in one session but two or three times since you are not on a flat surface when applying. Sand between finishing. When finished with that, I use to take the two part epoxy and fill in the small pores and any other depressions and give a final wet sandpaper sanding. At this point apply several coats of barrier coat. Depending on keeping in the water or trailering the boat will depend on applying bottom paint but remember some anti fouling paint properties will last up to 60 days out of the water while others will last on the anti fouling properties no matter what. In addition when storing any rudder with dark colors on a rudder, do so out of the sun as the heat build up in the rudder will be affected by direct sunlight. I hope this helps.
Never heard back from you but I appreciate your service in Army Aviation.