I have a old Gray Brand commercial transmission jack... Got it in the 90's when the shop I was working at was gonna scrap it... I asked & got permission to drag it home... It sat for another five years after that till I got a rack... Then it was time to see if I could get it working... Took it apart & found all the seals were rock hard & the main piston seal was completely disintegrated... Got the model & serial & stopped by our local Hyster Forklift/Gray jack retailer & asked about parts..... I was told my serial number couldn't be correct & without that they couldn't get parts... So I loaded up the jack & let them check the numbers... Turned out I was right & the numbers indicate it was the forty third transmission jack Gray built.... My transmission jack is older than I am... And naturally they couldn't get parts...
So I took measurements & opened my Hercules Bulldog catalog & matched up everything..... When I got the parts I put it back together & it's worked flawlessly ever since... Oh, I also bought a complete second set of seals & put them in the filing cabinet in a file titled "Transmission Jack"....
The first stage is pneumatic so you hook up air & step on the pedal... It'll lift a normal trans pretty quickly to about four feet... second stage is hydraulic & the handle is attached to the head so you don't have to reach down while looking up...
Point being older commercial stuff is worth looking at if your willing to do a little work..