You have the alternative of sourcing an aftermarket urethane u-cup as finding a seal kit may not be possible unless you have the brand/model for the jack. And even with that info, you still may not be able to find a kit.
In one of the pictures you see a number 40 on the bottom of the u-cup. That should mean that the outside diameter (OD) is 40mm. This is measure on the heel of the u-cup, which is the bottom of the u-cup, the one without the flared lips. To find out the inside diameter (ID) just measure the diameter of the metal part where the u-cup is mounted (see picture). You also need to measure the height (H) of the u-cup. Regarding height, you may or may not be able to find the same height you have but you still may be able to use a lower height to replace the one you have.
The usual way the numbers are represented when ordering an u-cup is: ID x OD x H.
Check the link below, you may be able to find what you need at a reasonable price. And while the pump is apart, you should replace the o-ring
inside the big nut. This o-ring is the one that seals the ram and they sooner or later have a tendency to leak. It should be metric (3.5mm) but you may be able to replace it with an 1/8" thick, or cross section (CS), o-ring as some sizes are interchangeable. Also, you need to measure the inside diameter of this o-ring. The way the numbers are usually represented for O-rings is: CS x ID.
If THEORINGSTORE does not has the u-cup size, check your local hydraulic repair shops, if they don't have any in stock they may be able to order one for you.
And if you are able, also replace the pump piston o-ring while you are at it. The wiper mounted on the big nut's outer end may be difficult to find, so don't worry to much about it.
http://www.theoringstore.com/index....th=690&zenid=cac5acc0dddc7e049d5c70c6dc0be0b1
