I used the google search above hydraulic air purge
and found this info in a related thread…
Members ChuckS and dieselguy share their knowledge…
Slide creep is usually but not always the result of the piston seal on one of the rams leaking by. Although it won't necessarily be on the slide that is creeping since all the hydraulic slide cylinders are looped together. You can go through the motions of tightening all the fittings, checking on all of the lines you can access, and cycling the slides completely in and out 3-4 times to bleed any air, but odds are it's a bad piston seal.
Either the Hydac valve on the front LG didn’t fully seat mechanically ( it’s normally closed when power is off via a spring ), you have air in the system , or you have an internal leak on one of the front LG
The LG are connected in tandem so what halogens to one happens to the other
I’d first cycle the front LG 3 to 5 times to purge any air out..allowing pump motor to cool off between cycles
Verify no external leaks at any of the JiC 37 fittings for the LG themselves as well as at the extend and retract manifolds
Check the manual over ride screw located on the end of the Hydac valve on the front LG..it should be snug CCW..
If issues persists then it’s a simple test to perform an internal leak bypass test