Can of worms it is!

As Mackenzie noticed an exhaust stud was going bald it was decided to take them out and replace them with nice new Stainless Steel Allen bolts. 
One came out .. .
Two came out .. .
Three came out .. .
Four snapped.

On closer inspection it showed that it has snapped before and had been really, really badly bodged before it got to CC HQ. A crooked helicoil did not help. 

First solution, weld a nut to the stud and put a socket on it. But it snapped somehow with around 6mm left protruding. Plan B, delicately grind a slot in the bolt and use an impact drive. But it didn't work. Plan C, easy outs, going well, stud snapped 8mm into the stud hole. Its not gone well for Mackenzie.

Chunks of the stud and helicoil.

A clean hole!

With the helicoli pretty much demolished it was drilled out. Next idea to solve it is weld it all in, drill and re-tap it. Or some kind of insert.