Rod seal or piston seal? If it's the rod seal, rebove the rod end from the pin and unscrew the rod cap off the cylinder and replace the seal and put it back together. If it''the piston then you'll have to pull the rod by remove the rod camp and pull the rod out and replace the piston seals AND the rod seal. Extend the rod almost all the way out before you remove the rod cap to minimize the ammount of fluid you'll spill.