I had the same problem with my SN. I got it for a great price and found that the shaft seal was blown. I took it off and the whole inside was destroyed. How I found it was leaking was just put it in the water and listened. You could hear water dripping from the back of the motor which then I took everything out and filled it with water and found the leak. You have already done that so I would take the water box off and inspect it. There is nothing bad with replacing the lines. It isn't that much and is always good to do with salt water. Great build and good luck with everything!