A couple more thoughts. You can look into the reservoir while the car is idling and watch return flow from the pump that constantly circulates, because the pump always pumps while the engine is running. If you don't see flow, I'd remove the pump and split it to see if it's ok. If someone ran it low on oil,the pump is toast, because it needs the hydraulic oil for lubrication.If the pump looks fine, I'd change the shaft seal. They can suck air.Seals are available;the rest of the pump parts are not. It's a little irritating to be able to take a nicely machined pump apart easilly and not be able to buy a new shaft bushing.

Good luck,
Peter

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