"A crankcase air leak can cause untold damage to your PWC engine. The best way to have a leak free engine and to maximize your engine's performance and reliability is by replacing your seals. SBT sells new crankshaft end seal kits to be used during the installation of a crankshaft to the case. These seals are durable and are made of high quality rubber and steel components so that they can withstand heavy abuse, pressure, heat, and oil. Center seals are not included in the crankshaft end seal kit."