So I got the head off. Hopefully my pictures come through below.
As I hope you can see, a 240d can be QUITE effective at crushing a nut. The damage seems to be out of the valve travel. (Valves aren't as big as the cutout.) The nut embedded by about .07" inches the top of the piston.

My questions: How thick is a piston? Is it likely to burn through if I run it? The walls don't seem scratched and #3 seems to have MORE wobble than #2 (the nut smasher) Is it possible that the impact slightly widened the piston?

Any thoughts would be welcome.

Thanks

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'83 300D turbo diesel (334k daily commuter)
SOLD '80 240D 4 speed manual, #2 piston pitted from crushing a 10mm nut. Running it 'till it burns through.
'78 F-150 300cid 4spd od (with my great unkle's original sales receipt)
SOLD '66 Ford P-350 delivery truck (almost driveable)
'49 Dodge B1D (1 ton Pilothouse era truck) not running but all there, candidate for om617 and 4x4 conversion when money permits.