Re: impeller problem
Years ago the copper interconnect tube was un supported and was slightly bent to keep it away from the drive shaft. It went from the top outlet hole of the water pump cover to a hole in the bottom of the engine block. It obviously was sealed at both ends. How depends on the engine. Looking up from with a flash light will allow you to see the hole in the block and the place where the drive shaft inserts. My current '02 90 hp, whose basic design was back in '89 when Merc quit the tower of production and went with 3 cyls, has a bracket to support the tube and it is a piece of cake to line up the hose when inserting the lower unit.
If you have water coming out from around your spark plugs you are getting water from your water pump to your block and your problem is a leaking gasket on the water jacket cover that has holes in it to allow it to fit around the spark plugs. The head in an integral part of the block (as far as I know...most Mercs are that way) so you just have a water jacket cover, not a cover and a head; one gasket not two.
Mark
