on the cylinders. is thare a common O ring for both pressure sides or is there cup seals back to back?
I don't know what control valve you have but they will be behind plugs on either side of where the oil comes out of the valve. Some are parallel to the ports others are parallel with the spool. Check behind the plugs, there will be one for each high pressure outlet. They will have a spring and poppet but some have a body thats part of the plug with O rings, my old 731 had this style and the o-rings were shredded, i replaced them and it was perfect.
I would doubt they just run O rings in the cylinders, they will be propper seals on the piston, i can't guess what style though. The rods will use a propper pressure seal. If you pull the rams down, take it to a hydraulic seal shop and they can match them for you.