Didn't see the crack there, BTW did you balance it again before doing the 300miles ?
When we did mine we took an old flywheel and cut it open, we then measured how thick the steel was(cant remember) and then worked out how much we could take off safely.
There isn't much steel there in the first place, most off the weight is the magnets.
Mine now measures 108mm, originally it was 110mm so its 2mm off for those who's maths aren't too great.
After that I got it balanced again and it did a full years racing with no problems and no cracks.