  A self-consistent version of the left-right (LR) symmetric model is used to
examine tree- as well as one-loop level radiative corrections to the muon
decay. It is shown that constraints on the heavy sector of the model parameters
are different when going beyond tree-level physics. In fact, in our case, the
only useful constraints on the model can be obtained from the one-loop level
calculation. Furthermore, corrections coming from the subset of SM particles
within the LR model have a different structure from their SM equivalent, e.g.
the top quark leading term contribution to $\Delta \rho$ within the LR model is
different from its SM counterpart. As a consequence, care must be taken in
fitting procedures of models beyond the SM, where usually, only tree-level
couplings modified by the SM radiative corrections are considered. This
procedure is not always correct.
