If all other hydraulics work and after you have replaced lots of stuff and only the bedroom slide doesn't work I can only give you my guess on what I would think it is and repair.
I think it is the actual bed slide piston has bad seals and the pressure is leaking around the seal instead of pushing it out.
To get to it you need to look under the bed and remove the thin piece of wood that is under the bed about halfway to the headboard.
It is just a cover and you will see the piston and the hoses.
Get the part number off the piston which will help you buy one if you plan to do it.
That is a small one and should be around $100 to $200 as a guess.
Link to page with all sizes and types.
Here is one that has only a 24" stroke meaning distance it goes out.
Yours may be less.
I would think at this point you could remove and replace or take it to a hydraulics shop to replace the piston seals inside.
This is all I can suggest for you at this time. I will try and find some pictures online to show you.