What was found
MAIN CABIN. TOP OF FLOOR STRUCTURE STA 959 LBL 49, CORROSION AROUND FASTENER HOLE. GROUNDED - YES. REMOVED CORRODED INTERCOSTAL I.A.W B737-800 SRM 51-40-02, LOCATED & DRILLED AND INSTALLED NEW INTERCOSTALL P/N 147A5660Y21 PER BOEING DWG #147A5660 REV C AND I.A.W B737-800 SRM 51-40-02. SRM 51-40-05, ORIGINAL MATL THICKNESS .080, REMOVED .012, REMAINING .068 FOUND TO BE OUT OF LIMITS IAW B737-800 SRM 53-70-51-1A-01.