Sierra 18-2599 Face Seal and Tool The Sierra 18-2599 Face Seal And Tool is interchangeable with the following: GLM 85590, Mallory 9-3628, Mercruiser/Mercury 26-816575A2. Each Sierra product meets or exceeds the original equipment part it replaces. Sierra Face Seal and Tool Meets or exceeds the original equipment quality Sierra part number: 18-2599 Interchangeable with the following: GLM 85590, Mallory 9-3628, Mercruiser/Mercury 26-816575A2