Three radiators replaced. Wow. How many engine hrs span this period? Your batteries are being over charged and/or your batteries are compromised and your voltage regulator is sending continuous current to your batteries. Lots of questions. Does your tractor sit for long periods of the year? You can neutralize the acid on your radiator with frequent baths of baking soda solution. Just a temorary solution. A robust battery will require less charging therefore less acid vapor. Could be your battery. Could be you voltage regulator. Really sorry that you have gone thru so many radiators.