  We study the quantizations of the algebras of regular functions on nilpotent
orbits. We show that such a quantization always exists and is unique if the
orbit is birationally rigid. Further we show that, for special birationally
rigid orbits, the quantization has integral central character in all cases but
four (one orbit in E_7 and three orbits in E_8). We use this to complete the
computation of Goldie ranks for primitive ideals with integral central
character for all special nilpotent orbits but one (in E_8). Our main
ingredient is results on the geometry of normalizations of the closures of
nilpotent orbits by Fu and Namikawa.
