There is probably no huge advantage to the Speedseal other than the use of an o ring rather than a gasket and the use of thumb screws on the cover. With the smaller Yanmar engines, there are two different raw water pumps used depending on where the engine was manufactured. The Japanese build has the water pump with the paper gasket, and the european build uses a Johnson pump which has a cover plate with an o ring (the parts are the same as the Westerbeke). Because the pump is mounted with the cover screws facing aft, removing the screws to change the impeller is a pain. Consequently, the easy way out becomes removal of the pump from the engine and changing the impeller at the workbench. Just replacing the original screws with thumb screws might make the job easier provided the impeller comes out without difficulty.