SE218 (Replaces Most Mercury 3.0L Counter Rotation)SE218 Replaces most Mercury 3. 0L Lower Units (SN 1B504989 and below). Does not replace the Torque Master, Torque Master 2 or the Sport Master. Available with a 25 or 30 inch (13 spline) 1 pc. driive shaft. If you have an 8 Spline drive shaft, you will need to buy the stub shaft unit and buy an upper driveshaft from an OE dealer. 25" 45 823901A 1 30" 45 824115A 1 (This item is no longer available from the OE. You will need to source a used one or fix