[Walt Fricke]

A good thing about using hex nuts instead of barrel nuts is that having a stud which sticks out too far isn't really a problem. A good thing about using reduced head flange nuts is that you can use a smaller (usually 12mm, but I see you can get 10mm wrench size M8 flange nuts too) wrench. All of this makes installing the header easier.

Me, I'd be inclined to leave any studs which behave when you remove the nuts alone. Breaking studs usually only occurs when trying to get the nut off, doesn't it? Having one fall out is unusual? Maybe when the thermal reactor were removed some of the threads in the heads were damaged, leaving the replacement stud or studs a bit loose? Those would be candidates for Helicoils or the equivalent.

Having one stud fall out ought not to interrupt a trip, should it? You didn't realize you had one missing? Might have been gone a long time? Low risk of interrupting a trip if one falls out?

Of course, those which feel loose ought to come out easily, which suggests a replacement along with the insert. And if you have them all out already, well why not new. But I'd not be inclined to go through the brain damage of working hard to get a stud out which resists removal.