  A maximum likelihood analysis of the NGC 4258 maser positions and velocities
reveals a ~2 sigma deviation from Keplerian motion in the projected rotation
curve of the high-velocity features, corresponding to a ~9 km/s, or 0.8%,
flattening of the LOS velocities with respect to Keplerian motion over the
range of the high-velocity masers. While there are a number of potential
explanations for this flattening, we argue for pure Keplerian rotation in an
inclination-warped disk based on the ability of this model to explain a number
of otherwise puzzling features of the system. A radial gradient in the disk
inclination of 0.034 mas^{-1} is not only consistent with the observed rotation
curve, but it generates a bowl along the near edge of the disk that naturally
explains the otherwise puzzling narrow spread in the declinations of the
systemic masers. It also explains the existence and location of an apparently
recurring flare amongst the systemic masers. There is no significant evidence
for non-Keplerian rotation in the inclination-warped disk. An additional
implication of the inclination warp is that the disk rises in front of and
obscures the central engine at a disk radius of about 8.3 mas, or 0.29 pc. By
comparing the observed X-ray column to conditions in the disk at this radius,
we argue that the molecular-to-atomic transition occurs just beyond the
outermost maser at 0.28 pc and from this we infer an accretion rate of
\~10^{-4}alpha M_sun/yr, consistent with the jet-dominated accretion models of
Yuan et al. (2002). Our model suggests that most of the observed X-ray column
arises in the warped accretion disk at 0.29 pc, and that the maser emission is
truncated at large radii predominantly as a result of the molecular-to-atomic
phase transition originally proposed by Neufeld & Maloney (1995).
