As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED ON TAKEOFF CONFIGURATION INDICATION ILLUMINATED AND MASTER WARNING LIGHT FLASHED ON AND OFF. LEADING EDGE SLAT ASYMMETRY EICAS AND LEADING EDGE LIGHT ILLUMINATED. RETURNED TO BOS AND LANDED WITHOUT INCIDENT. FOUND SLAT SENSOR S301 SLAT INBOARD TRACK FAULTED. REPLACED SENSOR. SYSTEM GROUND CHECKED NORMAL OPERATION.