What was found
(CAN) AFTER INSTALLATION OF A O/H ENGINE ASSY. DURING FIRST FLIGHT AFTER GROUND RUNS AND LEAK CHECKS THE PILOT NOTED TRANSMISSION LOW OIL PRESSURE FOLLOWED BY LOW ENGINE OIL PRESSURE. THEY DESCENDED TO LAND FROM 6,000 FT. UPON LANDING THE ENGINE CHIP LIGHT ILLUMINATED. THE MAINTENANCE TECH EXITED ACFT AND NOTED OIL ALL DOWN THE TAIL OF THE ACFT HE THEN SIGNALED THE PILOT TO SHUTDOWN. UPON INVESTIGATION THEY DETERMINED THE ENGINE OIL TANK HAD RUPTURED ALONG THE SEAM. SUBSEQUENT INVESTIGATION FOUND THE FWD PTO SHAFT SEAL 50 PERCENT INNER LIP WAS ROLLED OVER, SEAL, PN 406-304-104-101.