I'm not sure it's really fair to expect any company to be able to fix your machine based only on a phone call and some emails. You can't expect surplus center to take back a valve that is very much most likely working correctly. You also shouldn't expect to trouble shoot your machine for you by swapping parts till it works for no return hassle.
Might be time to take it to a hydraulic shop and get someone to look at it with you and troubleshoot it in person.
Were trying to help but you haven't posted any pics of what you have to help us see what you got, or checked all the pressures we asked for.
I've spent probally $4000 with surplus center in the last 10 years and always got what I ordered every time and it all worked. That doesn't mean you ordered the right thing or course. I wouldn't expect the phone tech help guy at SC to know all the answers.
