I've never had corrosion on either my regular BIIIs or SeaCore BIIIs, but my prop and ram anodes will last about 4 months before they are 50% depleted. I replace those in August and again when the boat is pulled in October. I use antifouling paint on my outdrives, which lasts about 4 months. If I don't hand scrape my outdrives and props every 2-3 weeks after August, I have barnacle growth. Do you have any pictures of the drives when the boat was pulled after a year in the water? With this type of maintenance the drives stay relatively clean and completely corrosion free. It would be impossible to do this type of maintenance between November and May up here due to the weather and temperature. So, that would be 7 months without an anode change and for growth to take hold. There are several other outdrives in my marina that receive no maintenance during the season. A few of them do not have any recognizable parts due to the growth. I can only imagine what kind of corrosion must be under the growth. My dock neighbor had twin BIII drives and kept his boat in the water the same duration as me last season, but without any maintenance of the drives. At the end of the season his drives were completely covered with barnacles an inch thick in some areas. There was no part of the drives that revealed any of the black paint. Mine had patches of growth in areas that I could not reach with the spatula from the dock. The service department at my SR dealer advised me against using Trilux 33 on the outdrives due to information they received at a SR meeting. It is thought that the metal content of Trilux 33 would cause corrosion. I don't know if they have evidence or are speculating. They used another product on my drives, but it was a spray-on thin coating, that gets me through only 4 months.