In the light of new absolute measurements of triple-differential cross sections for electron-impact ionization of helium we re-examine the various forms of the Coulomb T -matrix in the plane-wave impulse approximation. At higher energies the regularized form is supported by the measurements of Pochat et al while the Ford form is supported by the older, conflicting, measurements of van Wingerden et al. A revised calculation of the second-order Faddeev-Watson approximation is presented and compared with the measurements of Pochat et al.