To unstick a seized bolt like this (best example is vanos t55) you need to hit it firmly on the end of the bolt (as if it were a nail).

I recently twisted the head off two e12 m10 hardened bolts so I feel your pain. With a pin point torch you can heat just the bolt to make it longer and release tension on the threads

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)