[nzporsche944s2]

My trolley jack will jack the car up ok but it starts sinking slowly almost as soon as you stop pumping. For that reason I only use it to get the car high enough to put blocks under it.
I'm guessing it just needs new O Rings?
I've done some searching on the net and the jacks don't look that difficult to pull apart but I see there are springs and check valves in there too.

The jack I've got is an 3T old taiwanese one which is very solid and I'd like to save it if I can.

Can anyone tell me in generic laymans terms how to rebuild one? Or do I need to post a pic of it?

Thanks