Flex plate cracked

I'm running a 225 super slant six with a 904 automatic. I noticed a slight tick while idling and has recently become louder. It sounded like it was coming from the transmission so I decided to have a look this weekend. I took the inspection plate off the trans and found the flex plate cracked at all 4 bolt holes on the torque converter. I've never had this problem with any other Mopars so I have to wonder what caused it and how to prevent it in the future. I also need another flex plate which I believe is a 10" bolt pattern.