Old Leibherr 901 excavator Servo hydraulic problem

Hi
Just wondering if anyone out there can give some advice.I have used this machine for over 10 yrs and it has been great.
Last year it developed a problem with the servo hydraulics,all functions work but very slow response.
Checked the usual simple stuff filter,pump and pressures.Gave up and called Leibherr engineer in. He found a sticking spool valve corrected it but still said servo pressure was low.He could not cure the problem and said it could be the pump or something else.I think the age of the machine meant that the technicians did not have the diagnostic experience to detect the fault.
I want to have one last go at restoring the machine to its former glory. Have any old timers experienced this problem on old Leibherrs?
Any suggestions welcome.

Is the 'servo' system the same thing as a pilot system and does it have a relief valve?

Hi
Thanks for responding. I guess it is the hydraulic pilot system(servo) which controls the main valves and I know there is a small accumulator and pressure regulator on the system which holds pressure on the pilot system if the engine stops unexpectedly.My problem is the age of the machine,I cannot get a hydraulic system diagram and the Leibherr engineer who came out seemed lost in the old technology even with a diagram.I am sure it is something simple because all the controls respond on the pilot but with a delay and slow response.

if there is a delay and slow its probably your pumps not building enough pressure possible from wear. but it does sound like its your pump should pressure test them and check flow rates

I have seen the same in a 941, if my memory saves me right, it is 20 years ago, it was some sort of spring in the left hand lever there was broken, because of that it kind of only open the valves half way

Hi thanks
Have checked pressures and they are OK the problem does seem on the servo side of the cicuit.

Hi thanks for the suggestion, I will check the lever springs and let you know.