All hydraulic cylinders and swing are drifting fast as soon as you let go of the joysticks. If you boom up it comes back down. If your on a side hill the house will rotate down hill with out touching the controls
Sounds like your main relief is failing. Send me your email and I can send a diagrams. Do you have hyd gauges you can hook up?
No. Not main relief. No offense. Check hydraulic fluid viscosity, pull hydraulic filter and look for metal, open up hydraulic tank and look for metal. Multiple function failures typically won't have a single point of failure in common, though if that machine has pilot joysticks that could be an issue, does it change at all with the safety on? My first guess would be metal contamination holding port checks open or valve spools out of neutral.
It has pilot joysticks and hydraulic fluid and filter just changed. Rebuilt swing drive. Splines stripped out of coupler in the planetary section of swing drive.
Good day One school of thought if the machine has this fault when the fluid is at working temperature may be a filter- heavy fluid causing excessive back pressure. Kind regards Uffex