Fisherman

My guess here FWIW is the new sealing ring you fitted was a reject. From the regular shape of the hole it looks as if the counter bore was too deep leaving the wall there paper-thin. That thin segment would get red hot and curl up even at normal EGT's. You would not have noticed when you fitted it.

The seal ring in your Pic appears to be the old type, hardened with 6mm Dia. hole. These were later superceded by (seal-injector/617 - Pt.No.64760331) for all 616 and 617 engines. The new ones have a 10mm hole, are left soft and are 0.5mm smaller on the OD.

__________________
Beagle