fixing a hydraulic jack

i have a couple of inexpensive floor jacks that have gradually lost lift pressure this has been a slow process over several years so there are not any serious fluid leaks to repair, but the jacks are definitely loosing some fluid.

my question is, what is the best way to refill them? they all seem to have three points of access. the plunger for the handle, the bleeder screw at the bottom, and another bung by the plunger.

i have tried to fill one jack through the bng by the plunger and the bleeder screw with little success. i seem to need to pull out the piston to "suck in" the fluid and it seems to get pretty aerated in the process?

ideas?

Here's a tutorial on repairing typical floor jacks made overseas: http://www.garagejournal.com/forum/showthread.php?t=51105

hmmm. thanks! i looked through it and it is pretty helpful looking. sad to say that the "cheap chinese" jack in the illustration is heavier duty than mine..... but i will see what i can do with it.