As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FT # 1012, ORD-BOS. RETURNED TO FIELD. EMERGENCY DECLARED. SLAT FAIL CAUTION MSG AFTER TAKE OFF. SLAT STAYED AT 3. RAN QRH PROCEDURE AND SLATS REMAINED AT 3. LANDED SLATS 3 / FLAP FULL; REMOVED AND REPLACED #6 SLAT ACTUATOR IAW AMM 27-81-01 PERFORMED RIGGING AND OPERATIONAL CHECK GOOD.