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Distorted wave calculations of the triply differential cross sections for electron-impact ionization of He are presented for electrons sharing ≤ 50 eV excess energy (Ex) and having the coplanar, θ12 = π geometry. The results are in good agreement with absolute experimental measurements of T. Rösel et al. [Phys. Rev. A 46 (1992) 2539-2552] and of A. J. Murray, M. B. Woolf, and F. H. Read [J. Phys. B 25 (1992) 3021-3036]. For final state electrons sharing 2 eV excess energy equally, many-body perturbation theory corrections to the authors' first order (e,2e) triply differential cross sections [Phys. Rev. A 45 (1992) 4588–4603] are also presented. These results indicate that singlet-triplet interchannel coupling effects in the final state are very significant; that initial state correlations are significant near the perpendicular plane, i.e., θ1 = θ2 = π/2 ; and that the polarization effects we include are insignificant. Finally, comparison of our first order results with the semiclassical quanta1 theory results of D. S. F. Crothers [J. Phys. B 19 (1986) 463–483] shows excellent agreement for excess energies Ex ≥ 2 eV and for θ1 = θ2 = π/2; for Ex < 2 eV, the two results diverge as Ex → 0, indicating that experimental tests of the Wannier-Peterkop-Rau theory of three-body Coulomb breakup should be carried out in this energy region.