check your spring seats!

[erikv11]

He means if you can rotate the nut - the mount itself is not turning when you use the wrench. The collar has broken away from the rubber and is turning with the strut shaft.

You have every right to be frustrated, a strut job on a 150k car should almost by default include new strut mounts and spring seats. If your mechanic had experience with 850s then for sure he would have recommended it. I don't know if the spring seat design is different for GM etc, but I can guarantee you yours are broken on both sides. Or your mechanic/dad may be thinking of strut mounts, where the bearing is indeed designed to turn.

+1, if you are paying for the labor, then for sure get all four parts done now. Another thing in the strut assembly to consider at this time is the bump stops, if they are disintegrating then get new ones. No, you do not need to replace any of the mounting hardware.

Just to reiterate: The brand of the parts is very important here. If you buy non-Volvo spring seats, they will be worn out again within 15,000 miles and you will be right back where you started. Except about four times as mad. The strut mount there is a little more tolerance for aftermarket but if you want to be sure, buy the ones cn90 listed.