The HH5271 is the predecessor to the current HH5270. While many mechanical parts (like the tilt mechanism) are interchangeable, there are internal hydraulic differences.
The heart of the pump, where linear motion creates fluid pressure. Seastar Hh5271 Parts Diagram
Once you've reassembled using the diagram, here’s how to ensure longevity: Marine Part Retailers: Websites like eBay, MarineEngine