Wow! What a timely topic.
I have a 2012 390BH with the same problem where the dinette slide will even come out a couple inches when setting idle.
I have done some of my own diagnosing along with the help of Jamie fro Equalizer Systems. We proved the valve at the hydraulic pump to be good and is now suspect the hydraulic cylinder, namely Equalizer Systems part # 2368 that is allowing what is called "bypass", which lessens its holding power.
From my snooping around in the cargo compartment, I may have found why this particular cylinder goes bad. I believe there are some application design issues or installation issues. I found possible four issues.The hydraulic piston naturally is meant to go in and out as directed by the hydraulic pump. However, the dinette slide also goes up and down (a small amount) when the slide goes in or out. One end of the hydraulic cylinder is attached to the motorhome's chassis, while the other end is attached to the slide-out. The end attached to the slide-out goes up and down.
Possible Issue #1:
These attachments are not hinged and therefore the up and down motion imposes some bending force to the shaft. Not good, this can wear the piston seal.
Possible Issue #2:
The dinette slide is the longest and its hydraulic cylinder passes over the Freightliner longitudinal beam. It appears to me that when the slide-out goes out and down, it forces the cylinder to touch and attempts to bend it. Even putting a little ripple into the cylinder will cause it to bypass. This may be why FR changed the cylinder from 1.5: diameter to 1.375", to allow some clearance. See the note for part 2368......
Possible Issue #3:
When the slide-out is all the way in, the cylinder's rod goes upward. Right above it, crosses the timing rod. They do not want to touch. FR placed a plastic block mounted to the frame to prevent the rod from touching the timing shaft. This is good in a way, but in my RV the rod was pressing un-mercy against the cylinder's ram rod. I had to file some plastic away. This too, placed a bending torque on the ram rod and wear to the cylinder's seal.
Possible Issue #4:
When the slide-out is all the way out, the ram rod at the slide attachment is at its lowest elevation. Right where the rod passes through an access passage in the side of the motorhome (there is a brush seal there), it must not rub on the siding of the motorhome. Mine did not, but it is ever so close.
If the hydraulic piston only went in and out, that would be great; but because the attachment of the ram rod at the slide goes up and down, it makes for great difficulty in getting the very long cylinder and rod to traverse over beams and under the timing rod.
Back to why I said "What a Timely Topic", is because I have an appointment with a garage to replace the hydraulic cylinder and anti-creep valve on Oct 15th. I will let you know how I make out.
I sure hope that you all did not fall asleep on this on.