Cavity Slider Crooked Wall

Not entirely sure what way the wall is out of plumb. The unit needs to be dead square and plumb/level in its opening by using packers against the framing. The unit does not need to be dead plumb sideways though as you can really only keep them in line with the walls. It will perform better but 6mm out of plumb sideways is not a problem really providing the unit is twisted.

I have modified Corinthian units prior to install by cutting down either the framed unit side (closing side) including track or just the closing side track. Once it was necessary to cut 20 mm from closing side track as the door I was using was only 800mm wide. It would have had a 10mm gap at the back when closed otherwise. Another occasion I'd cut a unit down both closing and opening sides/tracks to allow a door to go back flush with the closing reveals.

What brand and size unit are you using? as there are many brands and a lot I've probably never used or seen.

Thanks for the response it is appreciated. The Wall is out by 6mm from top to bottom. So imagine if you were standing in the bathroom looking towards the opening for the door and the existing floor / wall junction was your starting reference point The existing wall leans away from you by the time you get to the ceiling by 6mm. The unit is supplied by CS Doors

I'd install it plumb, and use a moulding to hide the tapering gap on the bathroom side, and pack the sheeting out as needed to match wall on the other side.

cavity sliders are a PITAWAS as they are without installing them less than plumb