The S80's front seats tend to rock slightly - about 1/16" at the front. This is an acknowledged aspect of the adjuster design and for me showed up after several thousand miles. It is common enough that Volvo has a fix for it "for drivers that are bothered by the behavior" that involves installing a gas shock absorber inside the seat to damp the rocking accelerations. They will do it under warranty.

I must say that it works - even though the seat is still free to move, it feels rock solid.

The mod is available only for the driver's seat, even though both seats rock in the same way.

It is disappointing that Volvo wouldn't just add this fix to every new S80.

On another note, make sure that you NEVER lose your remote control. It cost us $230 to get a new one -

remote control - $110

software charge - $30

programming labor-$90

It takes about 10 minutes to program a remote control, but the standard service minimum for this operation is 1 hour. The $30 software charge comes about since you are adding an additional software element ( the new remote ) to the car's operating system.