  We compute isospin-violating meson-nucleon coupling constants and their
consequent charge-symmetry-breaking nucleon-nucleon potentials. The couplings
result from evaluating matrix elements of quark currents between nucleon states
in a nonrelativistic constituent quark model; the isospin violations arise from
the difference in the up and down constituent quark masses. We find, in
particular, that isospin violation in the omega-meson--nucleon vertex dominates
the class IV CSB potential obtained from these considerations. We evaluate the
resulting spin-singlet--triplet mixing angles, the quantities germane to the
difference of neutron and proton analyzing powers measured in elastic
$\vec{n}-\vec{p}$ scattering, and find them commensurate to those computed
originally using the on-shell value of the $\rho$-$\omega$ mixing amplitude.
The use of the on-shell $\rho$-$\omega$ mixing amplitude at $q^2=0$ has been
called into question; rather, the amplitude is zero in a wide class of models.
Our model possesses no contribution from $\rho$-$\omega$ mixing at $q^2=0$, and
we find that omega-meson exchange suffices to explain the measured $n-p$
analyzing power difference~at~183 MeV.
