Sierra 18-1957-1 Manifold The Sierra 18-1957-1 Manifold is interchangeable with the following: GLM 51240, Mallory 9-40506, Marine Power 0991-1000, Mercruiser 89011A8, 807078A6, 807078T10, 807078T09, 807078A4, 807078A2, Osco 9011. Each Sierra product meets or exceeds the original equipment part it replaces. Sierra Manifold Meets or exceeds the original equipment quality Sierra part number: 18-1957-1 Interchangeable with the following: GLM 51240, Mallory 9-40506, Marine Power 0991-1000, Mercruiser 89011A8, 807078A6, 807078T10, 807078T09, 807078A4, 807078A2, Osco 9011