The membrane is the heart of the watermaker, and if the membrane has been stored and unused for 5 years, you're taking a chance that it is no longer usable. *Since you have the operation and maintenance manual, perhaps you could first check what they say about decommissioning and storage of the membrane unit.
The RO membrane has a finite lifespan; if it were me, I'd assume it needed to be replaced and price my options based on that. *I think that you should first test the unit to determine whether the membrane has survived its storage and is functional, that the pump and all the seals are okay. *RO desalination involves high pressure, and you might find a fountain of water coming out of all the seals.
The Model 200 is an engine-driven unit, from what I can determine from the website. *What are your plans? *Would an engine-driven unit be the most appropriate for your purposes? *