A METRO 23 ON DSCNT AT 7000 FT DECLARED AN EMER AND SHUT DOWN THE L ENG DUE TO LOSS OF OIL PRESSURE AND QUANTITY.

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ON SUN/JAN/06 AT APPROX XA20 AM; I DECLARED AN EMER AND LANDED AT ZZZ. I WAS FLYING A METRO FROM ZZZ1 TO ZZZ. I HAD THIRTEEN SOULS ONBOARD AND WAS APPROX EIGHTEEN NAUTICAL MILES E OF THE FIELD DSNDING ON RADAR VECTORS WHEN THE L ENG LOW OIL PRESSURE ANNUNCIATOR ILLUMINATED. I VERIFIED THAT I HAD LOST OIL PRESSURE ON THE L ENG AND PROCEEDED TO SHUT DOWN AND SECURE THE L ENG PER OUR MEMORY ITEMS AND COMPANY CHKLISTS. I MADE THE DECISION TO CONTINUE TO ZZZ DUE TO MY CLOSE PROXIMITY TO THE FIELD. I THEN DECIDED TO DECLARE AN EMER TO ENHANCE PAX SAFETY BY HAVING RESCUE EQUIPMENT AVAILABLE AND FOR BEING PUT FIRST IN LINE ON THE ILS RWY 10L APCH. THE LNDG AND APCH WERE UNEVENTFUL AND AFTER I CLEARED THE RWY; I TOLD ZZZ TWR THAT NO OTHER SVCS WERE REQUIRED AND TAXIED TO THE FBO ON MY OWN POWER. I HAD AN IDENTICAL INCIDENT ON DEC/WED/2005 IN THE SAME AIRPLANE ON THE SAME ENG. ON THAT FLT I HAD NO PAX AND DIVERTED. IN BOTH INCIDENTS; THE LOSS OF OIL PRESSURE WAS DUE TO CRACKED STAINLESS STEEL OIL LINE FITTINGS. THERE ARE NO UNUSUAL VIBRATIONS IN FLT; BUT I HOPE THEY RUN SOME SORT OF VIBRATION OR HARMONICS TEST BEFORE THEY PUT THE PLANE BACK INTO SVC. THESE INCIDENTS ARE TOO CLOSE TOGETHER TO BE COINCIDENTAL.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT SINCE THIS WAS THE SECOND ENG SHUTDOWN ON THE ENG IN 10 FLT HOURS; IT WAS TIME TO LOOK FOR THE CAUSE. REPORTEDLY; DURING TROUBLESHOOTING; MAINT FOUND SEVERAL OTHER LINES AND FITTINGS NEAR TO FAILURE FROM VIBRATION. THE RPTR STATED THE PROPELLER WAS REMOVED AND FOUND OUT OF BALANCE AND WAS BALANCED AND REINSTALLED; ADDING THIS CORRECTED THE VIBRATION PROBLEM. REPORTEDLY; THE VIBRATION WAS OF A FREQUENCY THAT COULD NOT BE FELT OR SENSED THROUGH THE ENG CTLS OR AIRFRAME.