What was found
L/E SLAT ASSYM EICAS MSG AND ASSOC LIGHT ILLUM WHEN FLAP HANDLE PLACED TO ZERO. SLAT INDICATION STICKS BETWEEN 1 AND ZERO. PER FLT MANUAL IRREG 7-40 CYCLE FLAPS TO EXTEND, NO HELP. L/E ASSYM RETURNED UPON RETRACT SELECTION. PER FLT MANUAL DID NOT SELECT ALT L/E SYSTEM. AIRCRAFT RETURNED TO SFO. *S/D* NUISANCE MESSAGE GENERATED BY FLAP/SLAT ELECTRONICS UNIT (FSEU). REPLACED FSEU PER MM 27-51-01. RAN FLAPS AND SLATS TO FULL EXTEND AND RETRACT TWICE AND THEN ACCOMPLISHED BITE CHECK OF FSEU. ALL OPERATIONS WERE NORMAL AND NO FAULTS FOUND.