if you have one of those speed controlled drillers put a cutting circular fine tip and cut the box carefully at the joint between the 2 parts but do not go deeper than 2 mm as you will find the heat sink metal of the switching mosfet.After that try by hand with a fine knife slowly and you're done.
After the repair use SUPER ATTACK glue!!!
Oh....yes as techie said you have to cut it out. I did it manually with a fine hexsaw blade...on my Panasonic cordless adapter to replace its transformer!!! But unfortunately the gap grew wide enough to be glued again!! I don't really know why they ignore a scew type box.......
to give us more hard work! i also have many of this to disasemble and must be done with carefull to after glue it back. i just have some that after glued went for insurance and they never tell me nothing that was open so i assume they have not seen it was open before