I have heard that case IH uses certain additives in its oil that swells up orings and if you use any other oil they will shrink and start leaking. Is this true? Also, if you put some cheap oil in a case payloader and it started leaking, is there some sort of additive that might swell the o rings and seals and maybe stop the leaking? I've heard of people putting some brake fluid in their oil to do this but I wouldn't want to hurt anything permanently. Its an old 1994 case 921 loader.
Lots to unpack here. First, forget you've ever heard any silliness about brake fluid being added to hydraulic oil, it would be plain stupid. Second, Case 921 were originally speced for TCH fluid, now pretty much the norm is HyTran. I don't care what anyone else says, they are not the same. What do you have leaking? Cylinders or drivetrain?
Cylinders
Well, I can't speak for everyone, but on a 1994 loader, cylinders are going to leak, and they are going to go downhill fast if the machine has been getting limited use the last decade or so and suddenly starts getting it's bell rung repeatedly with production work. No oil or additive is going to stop a leaking cylinder. Maybe slow it a tiny bit, but not for long. Better get busy figuring out where you're going to take the cylinders to get repacked, and it's definitely not going to be your local Napa or ag dealer. Those rams are big, probably several thousand ft-lbs on the piston retainers.
See this THREAD . It should answer your question. The smart money says don't do it.