What was found
(CAN) DURING CRUISE FLT, RT ENGINE BEGAN TO LOOSE OIL PRESSURE. OIL TEMP & CHT INCREASED. PILOT ELECTED TO SHUTDOWN ENGINE AS A VIBRATION BECAME APPARENT & OIL PRESSURE DECREASED TO NEAR ZERO. AN EMERGENCY DECLARED & AIRCRAFT LANDED WITHOUT FURTHER INCIDENT. UPON INSPECTION, NR 5 CYLINDER & PISTON FOUND DAMAGED. PISTON FOUND WITH A HOLE IN SIDE JUST BELOW COMPRESSION RINGS. HOLE DOES NOT APPEAR TO BE CAUSED BY OPERATIONAL DAMAGE & ONLY 98 HRS TSO IS UNLIKELY. LOOKS LIKE A MANUFACTURING DEFECT OR SOME TYPE OF MECHANICAL DAMAGE. HOLE CAUSED CRANKCASE TO PRESSURIZE & THERFORE CAUSE ENGINE TO VENT IT`S OIL OVERBOARD THROUGH BREATHER TUBE. SAME AIRCRAFT & ENGINE EXPERIENCED SAME PROBLEM A WEEK PRIOR TO THIS EVENT BUT MAINTENANCE ACTIONS REVEALED NO DISCREPANCIES AS TO WHY OIL WOULD VENT THROUGH BREATHER. COMPRESSION TESTS WERE PERFORMED & REVEALED NO PROBLEMS & GROUND RUNS & OPS CHECKS COMPLETED WITHOUT ANY PROBLEMS. AIRCRAFT RETURNED TO SERVICE & OPERATED FOR 1 WEEK PRIOR TO 2ND EVENT WITH NO ABNORMALITIES INDICATED. CONSULTED ENGINE OVERHAUL FACILITY. DISASSEMBLED & EVALUATED ENGINE & DETERMINED ENGINE SHOULD BE REMOVED, DISMANTLED, INSPECTED, FLUSHED & REPAIRED PRIOR TO BEING RETURNED TO SERVICE.