Choosing the best Hydraulic valve material?

I am trying to manufacture a custom-made hydraulic spool valve. I ordered a valve that consists spool and poppet working together to a mold maker since there were high precision holes. It was disappointing because I run it at 50 bar and it worked intermittently. I couldn't understand what the problem was and I knew that the holes were not made accurately. The valve body was 4140 and spools, poppets were made of stainless steel. The bores are reamed and the poppets, spools were ground not heat treated.

Now I have been working with a different veteran mold expert and, he recommended to use GGG50 for the valve body and 115CrV3 for the poppets. Since I experienced the leak on the valve before, I gave up using spools to prevent further leaks. Now there are poppets because seat valves are more resistant to the leakage. Also, I won't implement any heat treatment on the poppets. The holes are being reamed and not important to be accurate as I use o-ring for no leak. It's being manufactured at the moment, so I cannot see if it works.

I want to manufacture spool valve later, but I wonder which materials are the best for spool, sleeve or valve body. I searched, however, I couldn't find enough resource. All I know is the valve body used as sleeve is made of cast iron and honed at last. The spool is made of aluminum or alloy steel. It is hardened and ground at the last phase to fit in the bore of the sleeve. I will be glad to know what is the order of heat treatment and machining phases.

Any help would be appreciated.

AS you have discovered commercial valves are cast iron body,spools are generally hard chrome plated ,and the steel not hardened at all,and quite easy to damage....Valves are usually quite complex inside ,not just simple spools,and IMHO ,beyond the scope of a not experienced person to design for a particular application..........so ,buy a commercially made valve with the specs you need.

Thank you for the advice.