How could you have damaged it so badly it can't be repaired??

It would seem you could either open the hole up and put some sort of threaded insert into the oversized hole or you could have the hole welded shut (they can weld AL) and redrill and tap a new hole...seems unbelievable that you would need to replace the entire head from trying to extract a glow plug even if you drilled too much.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz