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Well that isolates it to the swing cylinders and control valve. From what I understand, sometimes the spool in the control valve will stick in the center which sounds like a good possibility here. I don't know if it is a very common problem. There is also a check valve/ball and spring in the valve that could be weak or getting gunked up and bypassing. You can pull that out to check it. Look for a little bull plug and if it has a ball and spring don't let them fall out and get lost. I checked one that was sticking down, had a little trouble getting the ball to go in and then push it all the way in although it was more of a space problem getting my hands and fingers in there. Try tapping on the center part of the control valve while trying to make it swing and see if that unsticks the spool. You can also take your lines loose one at a time from the valve to see if you have flow when you are supposed to. Try this with the boom swung to one side and then later to the other. You would have to move it while you can and then leave it before it warms up. The IH 3120 does not show up as a valid model on the parts search for international at www.caseih.com or at the case construction website www.casece.com . Find the model # for the hoe on the hoe name plate and try the construction site. If so you can find a schematic and parts list. Also just put backhoe in the model search category and a number of them will come up. You will find a similar one so you have a picture. Just guessing, if the spool is sticking in the center, maybe it has a weak seal/orings. Works ok with colder heavier hytran, but once the fluid warms up and thins out, then it leaks by. Let us know what you find out. I know it is a lot of work to tear into these and take them apart and it is nice to know what is broken before you do.
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