  We report late-time spectroscopic observations of the Type IIn SN 1998S,
taken 14 years after explosion using the Large Binocular Telescope. The optical
spectrum exhibits broad emission features of [O I], [O II], [O III], H-alpha,
H-beta, and [Fe II]. The last decade of evolution has exhibited a strengthening
of the oxygen transitions, evidence that the late-time emission is powered by
increasingly metal-rich SN ejecta crossing the reverse shock. The H-alpha
luminosity requires that SN 1998S is still interacting with dense circumstellar
material (CSM), probably produced by the strong wind of a red supergiant
progenitor at least ~1000 years before explosion. The emission lines exhibit
asymmetric blueshifted profiles, which implies that the receding hemisphere of
the SN is obscured by dust. The [O III] line, in particular, exhibits a
complete suppression of its red wing. This could be the result of the expected
wavelength dependence for dust extinction or a smaller radial distribution for
[O III]. In the latter case, the red wing of [O III] could be absorbed by core
dust, while both the blue and red wings are absorbed by dust within the cool
dense shell between the forward and reverse shocks; this interpretation could
explain why late-time [O III] emission from SNe is often weaker than models
predict. The [O I] line exhibits double-peaked structure on top of the broader
underlying profile, possibly due to emission from individual clumps of ejecta
or ring-like structures of metal-rich debris. The centroids of the peaks are
blueshifted and lack a red counterpart. However, an archival spectrum obtained
on day 1093 exhibits a third, redshifted peak, which we suspect has become
extinguished by dust that formed over the last decade. This implies that the
"missing" red components of multi-peaked oxygen profiles observed in other SNe
might be obscured by varying degrees of dust extinction.
