After driving my perfectly running 1960 235 for three months it suddenly began running poorly during a 30 mile trip. I was nearly home at the time and eased on to the house. After pulling the valve cover I discovered two broken push rods. They were broken right at the rocker arm. Actually the cup that holds the rocker had a portion of the side broken out. One was worse than the other allowing the push rod to lean over and the valve was not opening. Both push rods were on exhaust valves. What could be the cause of this sudden failure and what could be it's fix?