The pedals I rebuilt (MKS EZY) had a keyed washer between the locknut and race. The keytab got chewed off because the socket turned the washer along with the locknut, seems I'd pushed the socket a little too far into the pedal. Luckily I had an old pedal to cannabilize another keyed washer from. So watch it and don't put the socket in past the locknut.

Also helps to have a thin-wall/deep-well metric socket the right size.