Hi Joe,
Yes, my flex plate not only developed cracks but basically disintegrated. Keep in mind that I was running about 300hp at rookie school for Reno. None the less, the flex plate was never designed to transmit the output of engine, just allow the starter to turn it over. The lightening holes in it alow flexing that initiated the cracks, then the whole thing shattered. Surprisingly, in my case the pieces happend to jam together in such a way that it still functioned until I happend to find it on inspection several flight hours later.
All the details of my fix are in the archives somewhere, but basically I replaced the flex plate with an off the shelf lightweight flywheel that I addapted to accept tracys damper plate. I took it to a machine shop to have the mounting holes correctly placed. I also had it balanced, but I probably could have skipped that step. I also had to machine a recess into Tracys mounting plate to allow the starter to reach the teeth on the flywheel. Details are in the archivees somewhere. That was going on in June July and Aug of 2011, which may make it easier to find.
Tracy also engineered a fix. His solution is in the archives too. He also seemed to think that the flex plate was good enough for a normially aspirated 13b, but after seeeing what happend to mine, I believe that even a n.a. 13b would eventually fatugue the flex plate into the same result. As I recall, at least one other person detected cracks in the same place.
Best,
Dave Leonard