We had a failing hydraulic pistion on our SOB, like you I thought the adjusting nuts were loose, they weren't.
If adjusting doesn't work ( with 2 to 3" freeplay) look for a shop that can rebuild your cylinder.
Or get a new one, here's a link to etrailer.
https://www.etrailer.com/dept-pg-Accessories_and_Parts-pt-Slide_Out_Parts-pc-Cylinder.aspx
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