also , pumps wear out, I have four that were given to my by a logging outfit as they were removed and replaced... they did not want the hassle of rebuilding or having them rebuilt.
most are gearrotor pumps ( like your engine oil pump) and if there is not a GOOD filter in the system they can become scored and worn .... pressure suffers as does system speed and response time. hydraulic systems should be rather self bleeding, but a spot of air trapped at the top of a ram will impart a slight delay ( the air will compress some before anything happens ) DO NOT try to bleed the system under pressure.... hydraulic fluid cuts like a LASER from a minor leak ( at least not by 'cracking" fittings,if there is a bleed port it my be designed to use under pressure....that is an unknown on my part ) I have a thread going about my PTO and I have a couple of pictures in it that may help you visualize what a PTO is and how they work ....
http://67-72chevytrucks.com/vboard/s...d.php?t=674960
good luck with the harvest!