Sierra 18-1931-1 Manifold The Sierra 18-1931-1 Manifold is interchangeable with the following: GLM 51630, Mallory 9-40901, Osco 5805, Volvo Penta 835804, 856883. Each Sierra product meets or exceeds the original equipment part it replaces. Sierra Manifold Meets or exceeds the original equipment quality Sierra part number: 18-1931-1 Interchangeable with the following: GLM 51630, Mallory 9-40901, Osco 5805, Volvo Penta 835804, 856883