Great Western Slab Saw Hydraulic Oil

The throttle valve has to be opened and closed for each slab. As the carriage is cranked back the valve has to be open and in order to hold the carriage in the back position the valve needs to be closed. The cross feed is turned to move the rock over for the new cut and the throttle valve is opened slightly to slowly bring the rock against the blade. After it makes contact the valve is opened further to control the speed. This all has to occur because the weight is constantly hanging on the carriage thus the throttle valve is constantly being operated and I suspect that the needle has a groove worn on it where it makes contact with the valve seat thus distorting the even flow of oil through it. The hydraulic cylinder moves very smoothly so I don't suspect that it is binding or such.
Bob