  A four-point function of $E_6$ singlets, of interest in elucidating the
moduli space of (0,2) deformations of the quintic string vacuum, is computed
using analytic and numerical methods. The conformal field theory amplitude
satisfies the requisite selection rules and monodromy conditions, but the
integrated string amplitude vanishes. Together with selection rules coming from
the spacetime R-symmetry \dksecond, this demonstrates the flatness of the
gauge-singlet spacetime superpotential through fourth order. Relevance to the
more general program of determining the (0,2) moduli space and superpotential
is discussed.
