This thing with breaking at or above the threads seems to be a more recent issue. When this happens, I believe that either you have to surgically drill and remove the remaining threads from the GP to salvage the threads in the head or just go after it with a drill, remove both the GP and the head threads and then repair it with a Time-sert or a helicoil.

I think more people need to try the "impact wrench set to low torque" method that's been discussed here from time to time.

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250