A friend of mine had this problem we are trying to solve. The studs where we install the header were stripped before. When we installed the turbo manifold, we realized that as we are trying to tighten the nut, the stud was coming back as we tightened it. We tried to make threads on it for a bigger stud (11mm) but since we tried to do it with the engine on the car, we had a hard time doing this.
The gasket on the turbo manifold blew within 1 week. We don't want to re-thread it for an even larger stud so what should we do?
Can we fill in the aluminum and make brand new oem size threads for the studs?

 

Helicoil is about all you can do.