Have a 2018 Komatsu D39PX-24 w/ 3000hrs on it that the blade will come on up on it’s own after letting go of joystick. Joystick does have some play/slack in it. It also does this during operation which stinks. Looking for suggestions on things to check. I’ve been told the joystick slack could be the issue.
Anyone have a suggestion?
Sounds like you have a spool valve sticking or not centering itself. It could also be compromised seals in the control valve. This could be a burr, shaving or other fouling matter, a simple spring centering adjustment, wear in the bore the spool slides in, etc. I don't know your system at all and aforementioned are generalizations. Regardless it sounds as if you have internal leakage in your control valve for the blade function.
Have you looked into any of the electronic blade control functions?
Were you able to figure this out I have a D51 ex-24 doing the exact same thing.