Ok guys,
I just went through this with my 25 year old sears floor jack. It is a quality unit that was made in Japan.
I took it all apart to check for the leak. The ball and spring valve were in good shape. If they are not, you can get a new ball from a bearing store.
The main shaft seal on my jack was cracked and was leaking internally.
This is what I did, I went to a hydralic shop to get a new seal. They told me the seal was not available and that I might as well throw the jack away. I am not a hydralics specialist, but I now one thing and that is jacks are made around seal availability not the the other way around. The jack manufacture does not make pistons and cylinders and then see if they can find a seal.
So I found a larger hydralics shop. I called them and they said they had it so I traveled the 40 miles round trip to get the seal. The box on the shelf was empty. They ordered another one and I had it in a few days.
The long and short of it is I had my jack repaired for $10. It took awhile to get the right seal, but I still have my good Sears jack.
The seal turned out to be metric, if you have an American made jack the seal will most likely be imperial dimensions.
Take the cylinder and the piston to the hydralic shop and they can match up a seal that will get your jack back under your truck doing the job it was made to do.
