$D_s$ Lifetime, $m_b$, $m_c$ and $|V_{cb}|$ in the Heavy Quark Expansion

We present some straightforward applications of the QCD heavy quark expansion, stated in previous papers [1-3], to the inclusive widths of heavy flavour hadrons. We address the question of the $D_s$ lifetime and argue that -- barring Weak Annihilation (WA) -- $\tau (D_s)$ is expected to exceed $\tau (D^0)$ by several percent; on the other hand WA could provide a difference of up to $10\div20\%$ of {\it any} sign. We extract $m_c$, $m_b$ and $|V_{cb}|$ from $\Gamma\ind{SL}(D^+)$ and $\Gamma\ind{SL}(B)$. The values of the quark masses are somewhat higher, but compatible with estimates from QCD sum rules; we obtain $|V_{cb}|\simeq 0.043$ for $\tau (B)=1.4$ psec and $BR_{SL}(B)=10.5$\% . We discuss the associated uncertainties in the $1/m_Q$ expansion as well as some consequences for other electroweak decays.