Once you have a lot of rust staining seeping out of your rudder, then the internal steel framework is on its way out. You can apply rustproofing & try to seal the cracks, but it is delaying the inevitable - it will have to be rebuilt or replaced. As metal rusts, it expands and is putting pressure on the inside of the fiberglass rudder walls. It will eventually open up more seams along the perimeter & allow more water in, accelerating the rusting & corrosion even further. Eventually the steel post will break off from the steel horiontal fingers running throught the rudder. You will know that its had it when the rudder breaks from the shaft & just spins freely, with no helm response. I have heard of folks cutting down the length of a rudder in a commercial size band saw so that the two halves of fiberglass could be re-used, once the post & steel framework were replaced. Not a cheap repair. I have never heard of your make of boat, but I bet that there are more then a few 25 foot boats out there in the yards that are left for scrap, but still have a decent rudder. I'm sure it's cheaper to replace with a salvaged used rudder then to rebuild what you have. Its up to you to decide to repair, rebuild or replace, before or after this happens. But considering that with no steerage you could loose your boat, & these types of failures always happen at the worst times (ie: storms) I would fix it now rather then later, or when its too late. On ounce of prevention.......
