Sierra 18-8366 Lower Unit Seal Kit for Honda BF75 / BF90 The Sierra 18-8366 Lower Unit Seal Kit is interchangeable with the following: Mallory 9-74000. Each Sierra product meets or exceeds the original equipment part it replaces. Sierra Lower Unit Seal Kit Meets or exceeds the original equipment quality Sierra part number: 18-8366 Interchangeable with the following: Mallory 9-74000