I know of 3 cranks breaking.
At this stage I'm not to concerned about it really, I have a feeling driving style may have contributed to 2 of them and the other was a earlier non factory turbo engine.
2 were with less power than mine has been making for the last 100k km.
I am sure there are others out there that have broken though.
Going to try aluminium flywheel to drop a bit of weight from the end of the crank (7-8kg), need to look into a few other ideas also, but touch wood, it will survive.
Never know untill you try these things.

Marty