He's some info I have. I have a service manual but I'd have to scan it and it would be too big for this forums file size rules. But will look thru it and refresh my memory.
My guess is the pump isn't fully bled. There are bleeding instructions in the stuff I'm attaching.
Any hydraulic supply should be able to rebuild that pump. Some are part of a logging supply and they rebuild all sorts of new and antique hydraulic parts, often without any manual. If you're near Longview, Woods Logging Supply.