As you can see this gasket should have been replaced long ago. Owners who do know about these filters often assume that because most of these pumps were installed after the primary fuel filter that changing the internal filter is not necessary.
This pump leaked due to a failed gasket and made a mess of the boat it had been in. It was also badly rusted and as such the owner made a decision to install a new one for his piece of mind and due to age and external condition.
Recognizing a good deal when I see one, I cleaned it and painted it and now use it as a portable fuel transfer pump. If it fails I will know about it and it won't fill an owners bilge with fuel.