  We analyze the steady planar shear flow of the modified Johnson-Segalman
model, which has an added non-local term. We find that the new term allows for
unambiguous selection of the stress at which two ``phases'' coexist, in
contrast to the original model. For general differential constitutive models we
show the singular nature of stress selection in terms of a saddle connection
between fixed points in the equivalent dynamical system. The result means that
stress selection is unique under most conditions for space non-local models
Finally, illustrated by simple models, we show that stress selection generally
depends on the form of the non-local terms (weak universality).
