The feed system works of pressure. SO... if it's leaking... you aren't getting oil. (as you seem to understand that) On the side of your engine... there is a small oil tank. Make sure that is full. There is a cap on it. Take it off, and fill it. Go run the boat, and the air (if any) in the feed lines will go to that tank, and the bubble will go to the top. (keeping the engine safe) Then fill that little side tank again.
You can loosen the cap on the side tank and start the engine to push the air bubble out... but I find that to be an absolute mess.