One point that has not been made: Make sure that the exhaust
flange, where it exits the transom, is properly sealed. On my boat, I have problem where I was ending up with a significant amount of water in the bilge, but only after motoring. I thought it was the stuffing box, it wasn't. I thought I had a raw water intake leak, i didn't. Then I thought that the exhaust
was leaking - it wasn't.
The flange that the transom, where the exhaust
hose connected to, wasn't sealed. When the transom squatted under power, water was leaking in around the flange. I removed it and properly sealed it. No more water leaks.