I am changing the impeller in the water pump on my classic 50. The last time I did this I had a really hard time getting the rubber seal to seal between the copper tube and the top of the pump housing. For some reason they put a notch in the top of the housing that makes it difficult to get the seal in. It has to fit perfectly or the water will not go up the tube to the engine. I saw that there was a washer missing between the rubber seal and the pump housing. This washer is cup shaped and I can't tell from the parts breakdown whether the flat back of the cup faces toward the engine or the propeller. I am thinking that the washer female part will receive the rubber seal into the fold. I may be backward though. Perhaps the rubber seal should seat against the flat side of the seal.