[Assimilator1]

Ah yea, I did see that, so they believe that a weak mixture melted the piston over time, then a piece of the piston broke off breaking a valve and entirely destroying the piston.
They state that no EML illuminated for the weak mixture (which would be concerning for all of us!).

That explanation for the piston breaking up seems odd to me.
I would've thought that if indeed there's a marginally weak mixture (enough to cause damage) then the piston would be slowly eroded/melted until either the piston is holed and compression lost, or piston lands melted and compression lost.
But my experience/knowledge with engines failing in this manor is limited, am I missing more unusual failures?