As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EXPERIENCED STRONG ODOR AFTER TAKEOFF. ODOR WAS EVIDENT THROUGHOUT CABIN AND FLIGHT RETURNED TO BOSTON. THE SOURCE OF THE ODOR WAS AN OIL LEAK FROM THE APU OIL COOLER ASSEMBLY AT THE IN OIL LINE UNION. OIL COOLER WAS REPLACED AND OPERATIONALLY CHECKED NORMAL.