What was found
(CAN) PART WAS RECEIVED AS AN O/H UNIT AND INSTALLED. ABILITY TO MAINTAIN DESIRED RPM WITHIN LIMITS DEGRADED QUICKLY. FINAL TEST FLIGHTS HAD MINOR SURGING AND HUNTING NOTED. ON REMOVAL, NOTED FUEL LEAKS IN THE DRIVE SPLINE, 2 SEALS, WASHING OUT THE GREASE SPLINES. ALSO NOTED, ASSY SPLIT LINES HAD FUEL SEEPAGE/LEAKAGE SIGNIFICANT ENOUGH TO CAUSE DRIPS. UNIT WAS REMOVED FORM THE ACFT, TO BE FORWARDED TO APPROVED SHOP. SERVICEABLE UNIT INSTALLED AND ACFT RETURNED TO SERVICE.