Cobra trailer hydraulic jack refurb?

My Cobra trailer hydraulic jack is starting to fail, to the point
where I now have to put a 2x4 board under the jack assembly to get my
wheel off the ground.

John Dezutti (7K) gave me some hydraulic fluid, but there doesn't seem
to be a good way to add fluid. I tried, and got everything *but* the
jack filled with fluid, and got no discernable improvement in
performance.

I'm also told that the hydraulic piston is exactly the same as some
found in automotive hydraulic floor jacks, and that I might be better
off just replacing the unit rather than trying to repair it.

Can anyone out there help out a fellow pilot with a limp er, jack?

Frank (TA)