hydraulic jack leaking from piston

[supermanotorious]

I noticed the bottle jack in my Harbor Freight motorcycle lift was leaking hydraulic fluid, I removed it, cleaned it, inspected the piston which has an O ring at the base, the O ring appeared to be fine. I refilled the reservoir (then ran around the house and restored several other bottle jacks to their former glory) and put the motorcycle lift back together. A while later I noticed it is still leaking. I suppose I should seek a new O ring and go from there, any other ideas?

 

[landuse]

Sometimes those O rings can look good, but they aren't

 

[TT540]

Maybe order a small assortment of O-rings and replace the factory with one a little thicker than what is on it. Does the jack hold pressure over time? If not, you may need to get into it far enough to find a check ball and perhaps that has some pitting or debree not letting it seal well.