Your pump will leak. Its suppost to. The thing is, its suppost to drip. Its by the packing on the shaft.
Now on my boat, the header lines were leaking, so I got a lot of water in. Not as much as you at talkin about.
Things ot check. The Transum adaper, the part of the pump that touches the boat, you will see a bunch of screws, make sure thay are tight. There is a nut on the other side.
IF you cannot find anything wrong, fill up the boat with water and see if you can see it dripping out in the driveway.
Hope this helps