Experimental and theoretical triple-differential cross sections (TDCS) are presented for ionization of the outer 3p shell of argon by 200 eV electrons scattered through an angle of 15ࠡnd for ejected electron energies of 2, 5, 10 and 20 eV. A distorted-wave Born approximation (DWBA) and a hybrid DWBA-R-matrix (DWBA-RM2) calculation both reproduce the shapes of the TDCS when the slow electron is ejected near the momentum-transfer direction. Near the opposite direction, the DWBA-RM2 model also achieves good agreement with experiment for the higher ejected electron energies, but discrepancies are observed for the lower energies. This three-way joint study emphasizes that it is essential to include a proper treatment of exchange in modelling low-energy ionization.