As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MAIN FUEL SUMP REMOVED FROM ACFT. TO FACILITATE MAIN TANK REMOVAL FROM ACFT. VISUAL INSPECTION OF INSIDE OF PART REVEALED CONSIDERABLE CORROSION ON BOTTOM INSIDE SUMP. AFTER CLEANING, OBSERVED ONE AREA WHERE CORROSION THROUGH WALL TO OUTERSKIN ON CASTING HAD ALMOST COMPLETE PENETRATION. UNABLE TO DETERMINE INTERNAL CORRODED CONDITION OF PART WHILE PART WASINSTALLED ON ACFT.