What was found
THIS IS THE 2ND AIRCRAFT I DID HAVE THE SAME PROBLEM WITH (FIRST ONE WAS N9873F CESSNA 402-0303 MORE THAN 10 YEARS AGO). THE VACUUM MANIFOLD (PARKER AIRBORNE DIV. P#1H5-9 S#10AT) FAILED DUE TO WEAK RIVET HEADS, IN ONE INSTANCE TOTAL FAILURE OF BOTH VACUUM SYSTEMS HAPPENED AT THE SAME TIME IN VMC, WHEN REMOVING THE MANIFOLD FROM AIRCRAFT (REMOVAL OF ALUMINUM LINES FROM VACUUM PUMPS) ALL RIVET HEADS ON BOTH ENDS FAILED AND MANIFOLD CAME APART IN 3 PIECES.