How to bleed a 4 ton floor jack?

[Eyegore]

As the title says I need help bleeding my floor jack. My floor jack is finally loosing its lift, I have not found any puddles of hydralic fluid though. And before anyone says it -YES I DO USE JACK STANDS ALWAYS!!! My dads boss was killed many years ago from a car falling on him so I know how important they are.
The jack goes back down even when there is no load on it so I'm guessing that I need to bled and perhaps replace the fluid. I've had this jack close to 15 years, I purchased it from a place called APCO and it has always been very reliable. The fill location is on top and I'm waiting till monday to get the proper hydralic oil for it but for now does anyone know the proceedure for bleeding it?

Thank you ahead of time.

Tom