Corrections of order $α_s^3$ to $R_{had}$ in pQCD with light gluinos

By a completely independent analytic calculation made in general covariant gauge we confirm the known result for the massless $\alpha_s^3$ correction to $R_{had}$ and check explicitly its gauge independence. We extend the calculations to include contributions due to a hypothetical existence of a colour octet of (light) neutral fermions known also under the name of gluinos.