As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE AC WAS IN FOR HEAVY CHECK FOUND CENTER FUSELAGE 3 PAX CABIN FLOOR STRUCTURE CORROSION FOUND AT UPPER SHEET BTW FR 85-86 AND LBL 12" AREA. MX REMOVED AND REPLACED UPPER SHEET BTW FR 85-86 AND LBL 12" AREA PN 170-86101-001 IAW SRM 51-43-04 SEE NRC 4000319-2000-0050 FOR WORK PERFORMED. AC RETURNED TO SERVICE.