My 1995 850 wagon needs new steering stabilizer links every 25,000 to 40,000 km. They express symptoms very similar to what you're describing when they're ready for replacement. The first replacement was required at 111,000km then again at intervals of 26,000km, 29,000km and 39,000km. Parts & labor to replace them ran around $225 CDN each time. The parts prices dropped for some reason so the last job was $175 CDN. The first replacement didn't last a year so the second was done under the parts warranty.

The car was bought used at 83,000 km and was moved to a harsher, bumpier environment. The previous owner's service records showed no problems so bumpy local roads may have revealed this weakness in the design.

Hopefully your S80 hasn't inherited the same flaw.