We have a 1997 century 612 top kick wrecker. We just acquired it. When we operate wheel lift from ground it would lift a truck to max lift but if we had it only A few inches off ground then go to lift again,hydraulics will not lift. Drop it to ground then it will go up to max again. We did have a pump input seal leak,which we replaced pump ,but it did it before also. That is why they sold it I believe. My question is ,do you think it’s leaking internally
in cylinder?previous owner had also replaced control valves as they say. The cylinder that tucks wheel lift up stalls out and also the tilt or lift cylinder also. (Not sure of the terms for each,sorry)or are there relief valves in question somewhere. Thank you