  The isospin-breaking vector meson decay constants are determined from a QCD
sum rule analysis of the vector current correlator $<O| T(V^3_\mu V^8_\nu)|
O>$, using a recently proposed implementation of the finite energy sum rule
approach. The analysis employs the three-loop version of the OPE, and two
different families of weight functions. It is shown that the requirement of
consistency between results obtained using these two different weight families
leads to a rather good determination of the parameter describing the deviation
of the D=6 condensate term in the OPE from its vacuum saturation value, and
that the ability to determine this value has non-trivial numerical consequences
to the analysis. The phenomenological relevance of the results to the
extraction of the strange quark mass and the determination of the $6^{th}$
order chiral low energy constant, $Q$, is also briefly discussed.
