Simple fix... No need to get someone else.
Resist the urge to install stock bolts or metal pins!
Drill some small holes in the inside around the shelf base and through it. Mix some epoxy (acraglass would be fine) with fibers to a fairly stiff paste.
Work the mixed epoxy into the crack and all around the break, across the shelf and up the walls of the inside of the stock.
SWEEP THE MIXED EPOXY OFF THE INSIDES OF THE BREAK.
Mixing some unreinforced epoxy for the break faces may be worth considering but probably is not needed.
Clamp and release several times to work some epoxy into the break faces. Reclamp and allow the epoxy to cure.
A little clean-up and you will be good to go.
art
