Another tip:
If the stud breaks off flush and if the drill bit wanders, I use progressively larger bits until I just start to hit the threads on the manifold. Then take a pick or drift punch and start bending in what is left of the stud closest to the manifold. There should only be the high part of the threads left so the stud isn't very strong at this point. After a while you will basically cave in one side of the stud and you can either unthread it or push/pull it out of the hole. It takes a while but has worked for me.
I hope that made sense.
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