Shauno it sounds as if the SEALS are passing within the pump, with no lose of fluid its probaly the main cause, when reving there is sufficent pressure build up to make it operational.
I,am not to sure wether there is a rebuild kit for it or may it might be worth having a look around that could be a cheaper option or even contacting your local subi dealer to see the availablility, if so have a go at replacing the seals yourself or get a mobile mechanic to come around and have the pump out for him before he comes, to save time and money.Cheers.

Nails