G'day Gents,
I've had two flap asymmetry events in over 35 years of flying both on B767s. One was a spurious warning and the system behaved as advertised and locked up, the other was a real failure of the torque drive tube to the outboard three sections of LE slats. In this instance the asymmetric override protection function failed and the LE devices went completely asymmetric with three quarters fully extending and the busted bits only just leaving the fully retracted stops.
Interestingly there was little adverse roll tendency. We weren't even aware that the protection function had failed and that the slats were actually asymmetric until after the aircraft was parked and shutdown.
Engineering investigation failed to reveal why the protection function didn't activate.
Regards,
BH.