What was found
(CAN) APU AUTO SHUTDOWN WITH LOSS OF OIL OUT DRAIN MAST REFERENCE ADDITIONAL WORKSHEET ITEM NR2 AND NR3. C/B CLOSED AT P91. APU REPLACED IAW AMM 49-11-00 THIS CLEARS MEL 49-1 AND MDDR 3227. PLACARD REMOVED. OFF APU PN 3800702-1SN P-6654 UNIT WAS ORIGINAL INSTALLATION FROM AIRCRAFT MFG. TSN IN APU OPERATING HOURS = 2256:30APU START CYCLES CSN = 2923 DAYS SINCE NEW = 562FOUR ADDITIONAL APU REMOVALS HAVE OCCURRED YEAR TO DATE ATTRIBUTED TO THE SAME CAUSE OF TURBINE BLADE WALKING. OEM SB131-49-7860 REFERS. ADDITIONAL OEM DEVELOPMENT IN PROGRESS FOR LONG TERM CORRECTIVE ACTION PLAN.