  We compute the renormalization mismatch displayed in 1--loop approximation by
classically equivalent 4-quark operators and coming from different possible
definitions of the $\gamma_5$ matrix in dimensional regularization. The result
is then employed to study the effect of the various treatments of $\gamma_5$
upon the size of radiative corrections to 4-quark condensates in the QCD sum
rules for $\rho$ and $A_1$ mesons. We find that a fully anticommuting
$\gamma_5$ which automatically respects non-anomalous chiral Ward-Slavnov
identities leads to considerably smaller corrections and reduces theoretical
uncertainty in the QCD prediction for the $\tau$ hadronic decay rate.
