  A new approach with BRST invariance is suggested to cure the degeneracy
problem of ill defined path integrals in the path-integral calculationof
quantum mechanical tunneling effects in which the problem arises due to the
occurrence of zero modes. The Faddeev-Popov procedure is avoided and the
integral over the zero mode is transformed in a systematic way into a well
defined integral over instanton positions. No special procedure has to be
adopted as in the Faddeev-Popov method in calculating the Jacobian of the
transformation. The quantum mechanical tunneling for the Sine-Gordon potential
is used as a test of the method and the width of the lowest energy band is
obtained in exact agreement with that of WKB calculations.
