Let me start by saying that when I first started using it the boom stayed correct. But now after about 5hrs of use it now leaks down while operating. I've repacked both boom cylinders so that's not the concern. What else should I look at?
Sounds like your control valves are leaking thru.
You will have to isolate the problem, the seconday and check valves Orings could have failed, this can be checked by getting some JIC caps and plugs, #12, I believe, capping the lines that go to the valve and lifting the dipper to put pressure on the boom circuit. If that stops leakdown the valve is the culprit. If the boom lowers the cylinders are at fault. Gheck the barrels for damage in the area where the stabilizer pad would be if the boom was swung over with the pad up. I have seen way more bent dinged cylinder barrels causing packing and piston damage and leakdown than valve problems.. Mel