Kate....

BTW, if the head is Aluminium, it may be that the torque was such that it's 
stripped, not cross threaded... Little difference since either one will 
result in the need for a thread chase with the proper tap (minium) and 
possibly a Helicoil (even if the head is steel).  

Yes, the culpret deserves an infestation of a thousand sand flees in all 
critical cavities.

More ???'s anytime.

John Carey