If it is ABS, we in Apache-land are very familiar with the cure.
MEK and what we call 'Goo', MEK and ABS pellets mixed together and injected in the crack will do the trick.
Make sure to clean the affected area thoroughly.  Brush the MEK along the edges of the area.  Using a syringe filled with Goo, squirt it in and feather it along the MEK softened area.

An emergency source of ABS is computer keyboard shells and keys.  I've got a goo solution of cream colored keys and MEK/PVC glue.  It's getting harder and harder to find true MEK due to the meth labs.