A potential assembly problem on Lycoming four and six cylinder, dual magneto engines with rear mounted propeller governor drives could result in loss of engine oil leading to an engine failure. The oil loss results from the omission of a plate, Lycoming part number (P/N) LW-12347, which is required between the propeller governor drive pad and the propeller governor. The plate is only 0.040 inches thick and could be mistaken for a used gasket and discarded with removal of the propeller governor or shipping cover. The plate is actually a spacer to position the propeller governor away from the propeller governor drive pad. Without it, the propeller governor shaft might make contact with the bottom of the gear assembly inside the rear accessory case and prevent the propeller governor drive pad and the propeller governor flange from being drawn together to compress the gaskets. If the gaskets aren?t compressed, they will not form a sufficient seal, which could cause an oil leak. For the full text of the service bulletin, click here and open SI-1438A.