I have an old Snap On YA642 jack. I bought it new in the early 80's, it's one of those made in USA by I think Walker who also made the Lincoln version, they all look the same. It hadn't worked for years and I had bought other jacks in mean time, intending to get the parts to fix the old Snap On one day. We'll one of the replacements I bought started leaking so I looked into finally getting the parts for the Snap On to fix it myself. I have the A series version of the jack and apparently the tank nut can be a bear to remove. It requires a special socket, probably need to fabricate one out a big impact socket. Anyway, I called a local hydraulic repair shop that advertises it also repairs jacks.
I call them and first thing the guy says is if it's USA made it should be no problem, he has the kits.
Long story short, I drop the jack off and he calls me next day, it's done. Go pick it up and its all cleaned up, lubed and even a new metal vent cap to replace the original plastic one. Parts & labor - $150. Well worth it.