I'm leaning towards cooling system problems and overheat now that Mike said he had the cooling system block and flush at ~5,000km. I posted this on 4BTswaps:
The cooling system may be the culprit. Running high (but normally manageable) EGT with cooling blockages in the centre of the block could make that piston overheat, swell and grab the bore. Resulting in all the piston/bore scuffing.
It's not melted from the top like the average stupid EGT failure. The cracking and piece missing could be a rough history combined with overheat and loss of strength from the overheat/fire.
The cooling system may be the culprit. Running high (but normally manageable) EGT with cooling blockages in the centre of the block could make that piston overheat, swell and grab the bore. Resulting in all the piston/bore scuffing.
It's not melted from the top like the average stupid EGT failure. The cracking and piece missing could be a rough history combined with overheat and loss of strength from the overheat/fire.