What kind and how many miles ?
My Sears jack started a very slow leak-down with the bike on it so I made sure I stopped the lift just above the welded stops. This was the second year with the jack. Looking at the owners manual I found they want the owner to change the oil every year

. The jack was getting worse so I bought a small bottle of hydraulic oil and did the change. I was happy I had a new jack after that change. Seems I read the air can be trapped during the mfg.
Typing this I think it's been 2 years since I changed the oil

the bike has been on the jack all winter. I do place a small jack under the Sears just a back-up for winter storage.