I've not rebuilt one. I've seen seal kits on eBay but nowhere else really. They must be out there somewhere. Before going to the effort just check that the shaft of the hydraulic ram has no damage to the chrome plating, rust, corrosion etc. That's often what causes the seals to go. You can get them polished and re-plated but it's about $300 last I checked (which was admittedly like five years ago).