Astro Flywheel

My 1996 Astro Van has been breaking flywheels. This problem started at 65,000 miles and I am now up to 6 flywheels at 140,000 miles. They break from the center out and the teeth are not damaged. Chevolet and local mechanics cannot find the problem. I have replaced the starter and the torque converter at different times trying to resolve the problem. Nothing seems to be misaligned. The dealer suggests that I might replace the transmission but he gives no guarantee that this will solve the problem. I only recently found out that Chevrolet had replaced the transmission when the car had only 94 miles, however they refuse to provide me with the reason for the replacement. Has other owners had problems with breaking flywheels?