  We consider the sneutrino resonance reaction l^+ l^- -> sneutrino -> tau^+
tau^- in the MSSM without R-parity. We introduce new CP-violating and
CP-conserving tau-spin asymmetries which are generated already at the
tree-level if there is sneutrino - sneutrino-bar mixing and that are forbidden
in the SM. It is remarkable that these spin asymmetries can reach ~75% around
resonance for a sneutrino mass splitting of \Delta m ~ \Gamma and ~10% for a
splitting as low as \Delta m ~ 0.1\Gamma, where \Gamma is the sneutrino width.
We show that they are easily detectable already at LEP2 so long as the beam
energy is within ~10 GeV range around the muon-sneutrino masses and may
therefore serve as extremely powerful probes of sneutrino mixing phenomena.
