I recently replaced the impeller and gaskets on my 1994, Mariner 2 stroke, 90 HP. When I pulled the lower unit and shaft there was no rubber "O" ring on the shaft next to or on top of the impeller cover. Is this normal? This is the first time it was replaced. I assembled it back together and it seemed to work fine and pump water. I talked to other boat shops and they said it if that's the way it was it was ok. I don't see how an "O" ring would serve any purpose on there, because the hole up where it would fit when assembled is bigger than the "O" ring and the ring would just sit on top. 