Epoxies are not all the same and if he would have used the West System epoxy, I wouldn't be posting this. West System gets very hard unlike regular two part mix that dents easily with a finger nail and can creep under tension. When Colloidal Silica is added to the mix, it also provides gap filling strength. It can also be tinted with Trans tints, which helps the finished job look better. If there are equals to West System, I am not familiar with them and will only use the West System for any instrument work where epoxy is determined to be the best choice.
I took images along the way to share with the mandolin's owner and thought I would post my process for anyone interested. I didn't take any before images but the only thing relevant I can add is that the entire head stock, front, back and sides, was sprayed out rattle can Black.
I heated the once again failed repair and it rather easily came back apart. The next step is to use dental tools, Exacto knife, whatever to mechanically remove as much glue as possible. This step is important to not only get the parts to fit back together correctly but also to ovoid gluing glue to glue as much as possible. You can see that there isn't much to work with...
