The extraction of a 120 GeV proton beam from the SPS with transverse particle diffusion onto a bent crystal deflector has been considered with computer simulation. The asymmetry of extraction efficiency with the crystal orientation relative to the beam direction was observed. It was shown that the crystal deformation in the vertical plane led to a considerable broadening of orientational dependence and also a broadening of the extracted beam and its split. (author). 9 refs.; 11 figs.; 1 tab.