As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT GROUNDED FOR HEAVY MAINTENANCE. AFT LOWER CARGO INTERCOSTAL IS CORRODED AT LOWER SURFACE BETWEEN STATION 1263-1286 LEFT BUTT LINE 22. INTERCOSTAL BETWEEN STATION 1263-1285 AT LEFT BUTT LINE 22 WAS FOUND TO BE OUT OF LIMITS. INSTALLED NEW INTERCOSTAL IN ACCORDANCE WITH SRM 51-40-02.