[AT] Hydraulic bottle jack issues

[David Trompower]

need your thoughts and help with this.
 My  old Black jack  brand, hydraulic (bottle) hand jack, 12 ton model,   will  raise the ram,  but not retract the ram. 

1) Opening the release valve does nothing. 
2)  the weight of what I have raised with the jack  will not  push the ram back down? 
3)  I can stand on it  and it will not retrack.
4)  if I hit  the ram  with a mallet it will slowly go down, .. an 1/8 of an inch  with each blow is all. 
5)  Left over night with a load on the ram,  will not cause the ram to be retracted by morning.
6)  I opened the filler port expecting there is too much oil or excess trapped air.  but neither came out?

What is wrong?
 What  would you  recommend I do to fix this jack?
I am stumped. 


R. David