I have a circa 1989 Kubota B7200 HST with an "RC60-72H" 60-inch belly deck. I started using it April 2008 when it had 846 hours. In Sept. 2010, at 935 hours the middle blade broke. Then again at 956, 960, and 965 hours. So the middle blade has snapped four times - 3 x with old blades, once...