I had a thought which is turning into a suggestion. Before you going ripping things apart found out whether that hydraulic cylinder has a drain line on the seals.
We had a hydraulic leak on a SL10 recently just after installing a new pump. The leak was from the drain line returning seal leakage to the tank. High pressure high speed rotating seals are often designed to be leaky. This is for a couple of reasons: If they do have components actually in contact the contact forces from the pressure combined with the high speed makes things hot so the leakage provides a cooling flow. The other reason is that sometimes these seals do not have any sealing surfaces in contact; they have what is called a labyrinth which is sort of mini-size interlocking grooves and ridges with very small clearances but no actual contact. The fluid can escape through the small clearance but it has a tortuous path and when the seal is rotating this enhances the turbulence in the leakage flow so it is quite small. All that is needed to maintain pressure is a pump large enough to overcome the leakage flow. And naturally there has to be a system to collect the leakage and return it to the tank.
An open mind is a virtue...so long as all the common sense has not leaked out.