Took out the baffle then pushed the flat steel bar with the bolt through the hole in through the silencer end. It went easy as the opening is about30mm across. Then held the bolt head with a longish 13mm open end spanner.
It would have been useless just welding the stud back on with the vibration produced by a Triumph twin. It was brazed anyway when new. Not ideal to have a one bolt fixing and most silencers i use have a rail and use two bolts.
The other side will fracture next. I have already welded that side up but it is doomed.