you need helicoil kit size M10. Try to get oversize helicoils as the ones in the kit are 15mm long, I've found that 20mm long will fit very nicely, these are about 50p extra but are worth it. The correct size drill bit is 10.4mm. If its worth doing, its worth doing right.

I would'nt bother trying to remove the old stud if its seized solid, just drill and tap it. As I said, the whole kit cost me £45 but the helicoil has taken the 110Nm torque with no problems.