Actually it IS the cables that pull the side out and in.
When OUT, the cables on the outside are slightly slack. About an inch of play as it was the cables on the inside that PULLED to move the slide out and would be tight.
When you bring the slide IN, the outside cables are PULLED to move the slide in. Thus the inside cables become slightly slack.
But yes, these same cables also account for tops bottom and side skew thus keeping it all square. And if ever adjusted, their are moved in pairs. (Adjustments are inside the rectangle boards above the unit and not the best place to work with them.
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On a side note, if the motor ever gives out, you can open up the center panel to get to the motor and use a cordless drive to spin the shaft that drives the gears to move it. Up in that area you should find the bendable bit for it pull tied to a screw. You have to look for it.