Based on the porous nature of the bond and the fact that the broken bond resembles stressed ABS, I suspect solvent welding.
That's bad news; this is worse: the glue is strong enough and the shell is weak enough that breaking they glue in the usual way (attack with wedge, then pry shells apart) can cause visible damage to the outer shell. Dremeling away part of the inner shell would probably be a wiser approach.
Given that the Demolisher is the second recent blaster to sometimes have inconveniently placed glue - and that there have been many blasters which exhibit significant variation presumably depending on serial number - I wonder whether it would be a good idea for us Nerfers to always specify the serial number of our blasters whenever discussing internals and such. This would make it easier to keep track of these variations, but I'm not sure how useful this would be in the end, as a blaster's serial number usually can't be seen before purchase.
Pictures after the jump: