  Strong upper bounds are derived on certain product combinations of lepton
nonconserving couplings in the minimal supersymmetric standard model with
explicit $R$-parity violation. The input is information from rare leptonic
decays of the long-lived neutral kaon, the muon and the tau as well as from the
mixings of neutral $K$- and $B$-mesons. One of these bounds is comparable and
another superior to corresponding ones obtained recently from neutrinoless
double beta decay.
