lFrom what you showed, seemed a very possible cause. Better to do is call Mugen and tell them what happened, look if they allow it to send as RMA for inspection and repair... a bearing failure is very strange... how much fuel did it pass thru the piston?

If not, go ahead and put a TKO main bearing and re-sleeve it (sh*t happens everywhere... happened to me some years ago with only 1 litre of fuel), put one on one R01 from the past season (test mule) and is a cheap and great bearing (just be aware that ceramic bearings are quite different animals and need some tanks babying just to ensure that are properly seated... don't install it and go balls out to the track another time.. ).

In the next days I'll contact with Peter just to order more of their bearings to being TKO'ed all (and are a bunch the pending ones... ).