Slide out slipping

[LasVegasEnnis]

Has anyone had this issue. After parking and storing my 3596 Big Country I come by a few days later and my drivers side living room slide is extended two to three inches. I retract it completely. The same thing happens. Any ideas? I'm thinking a hydraulic check valve is leaking (no leaks of any kind around the pump).

 

[NYSUPstater]

Hydraulics. Our '06 Cedar Creek would do the same thing after sitting all winter inside. Cycle again and all was well.