What was found
DURING ENG TEARDOWN, 1ST STAGE DIFFUSER CRACKED & BROKEN AT INTERSTAGE SEAL BORE / WALL. IT APPEARS THE WALL SECTION WAS MACHINED UNDERSIZE IN THIS AREA CAUSING FATIGUE CRACKS TO DEVELOP & A LARGE PORTION OF PART BROKE OFF. BROKEN PIECE FELL INTO REAR FACE OF 1ST STAGE IMPELLER CAUSING A LOUD INTERNAL RUBBING NOISE. ENG REMOVED FOR REPAIR. 1ST STAGE DIFFUSER INSTALLED IN OVERHAULED CONDITION & HAD 3625.6 HOURS TSO AT TIME OF FAILURE. NO OTHER WORK DONE IN COMPRESSOR AREA OF ENGINE SINCE THE TIME OF INSTALLATION. PIECES & SHRAPNEL FROM FAILED PART ENTERED PRIMARY GAS PATH CAUSING IMPACT DAMAGE & RUB DAMAGE TO DOWN STREAM COMPONENTS. MAJOR RUB DAMAGE FOUND ON 1ST STAGE IMPELLER & 2ND STAGE COMPRESSOR HOUSING.