240 has the hic-ups

Funny you should ask this question. I have a 240 with the same problem and I plan on working on it this weekend. I asked a similar question a couple of weeks ago and received a response. The print-out I have of the reply doesn't have the name of the respondant on it so I can't give credit where it is due. His relpy to my inquiry is as follows.
"From your description I suspect that you have an obstruction in the line going to your cylinder. If the enginer gets loaded up when you raise or lower the lift without anything on it, chances are that the pump is putting out high pressure which isn't making it to the cylinder because of an obstruction, and the system's high pressure relief valve is (correctly) relieving this pressure before it gets dangerously high - but putting out this high pressure makes the engine work hard. If you don't notice any difference between how the system acts in the middle of the cylinder's travel and at the ends of it's travel, an obstruction is almost certantly the problem. Another tip off is if the rate at which the cylinder moves is very slow. The obstruction could be in the control valve somewhere. If you have more than one circuit in your hydraulics, a check of how one performs verses the other would be informative."
I do have dual system on my 240 and the other side works fine. I did rebuild my control valve and it didn't buy me anything. Next is to flush the line to the rear and rebuild the check valve under the seat (I think that's what it is)
Keep me updated on your progress. It may help both of us. Does anyone know how hard it is to rebuild the cylinder?

regards,