Originally Posted by Hoverbod

Screw extractors are useless if the blot has sheared because it is rusted in. If the screw was tight enough to shear the screw head off, in 90% of cases you will just snap the extractor, and then drilling it is nigh on impossible.
I would drill it out, start with a new 3mm drill and get it as straight as possible, then drill it 5mm, and then re tap M6.

Jamie