You just need to put enough oil back in to cover the pump.
With the lift lever in the raise position, the arms should steadily go up, and stay up, even with the engine off, until the lever is returned to the lower position.
I say "stay up" as in hold their position with only a gradual creep down. The lift cylinder has steel sealing rings that don't seal perfectly, even when new, so there will be "some" leakage.
The pressure relief valve is screwed into the right rear of the pump. If oil is moving in that area, it's the valve. BUT DON'T REACH IN THERE!!!