I wonder if he's talking about the heat exchanger, which has plates on both ends, but it's not a pump and doesn't have an impeller. Heat exchangers do need to be serviced regularly, and are hard to remove cause the hoses never come off easily.Ah. That's the original fuel filter, I think, on the side of the engine. My impression is they are frequently replaced with with a Racor unit mounted for better convenience, because old boats have crud in the fuel tank and filter changes become periodic preventative maintenance.
Some of us here have the 5411 and will know more.