Usually you will see a return filter, and maybe a suction strainer, but I dont think I have ever seen a filter on the pressure side of a hyd pump. Usually a return filter is all thats required. This should catch any fine trash going thru the system. This will usually be a 10micron filter. A suction strainer is usually a little more open and is designed to catch any bigger particles that might get in the oil and could damage the pump. If you have a screen on the filler port of the hydraulic tank, there shouldnt be any large pieces of trash in your oil. Only filters I have seen on the pressure side of the pump are usually the brass type you described and are usually on load sensing valves that have very tight clearances and minute particles could cause sticking. I dont think you would have/need that kind of hydraulic system on a wood splitter. If you remove the current brass filter and added a screw on filter in the return line before the tank, it should work fine.
