The non-unitary model operator approach, which has been previously used for calculating the binding energy of closed shell nuclei for central potentials, is formulated in a way suitable to realistic potentials, such as the Hamada-Johnston and the Reid soft-core ones. The factor-cluster expansion, truncated at the two-body terms, together with a 'healing condition' is used. The Euler-Lagrange equations which result from the application of the variational principle are integrodifferential and two kinds of coupling appear: one because of the tensor potential and one because of the non-unitary model operator. By solving these equations numerically for 4He, the binding energy of this nucleus is obtained for various values of the harmonic oscillator parameter and saturation is observed. The results are superior to those obtained with the simple (central) Kallio-Kolltveit potential and the 'healing condition' but for those the author used the Euler equation resulting from the (left) 'unitary' model operator approach.