Refurbishing for aesthetic as well as safety reasons or repairing after accidental damage. Either way this component and some of those listed below maybe required:
Renewing all the parts of the assembly will look better, and probably work better, than mixing old and new parts.
Add as many new items as you wish to the same shopping cart, nice new shiny fasteners would look better than reusing the old ones for example, and still only pay the same single fixed price shipping cost.
Don't forget to order a new Reservoir cap and diaphragm?