Thanks for the responses.

As far as what part failed... I'm going by what the mechanic told me. I gave him strut bushings, ball joint and tie rod as possible parts to replace. He said those were not the problem, and either the strut housing is bent or there is an internal problem with the steering rack. ???

Strut mounts? I had new upper strut mounts installed when new struts were installed about 15k miles ago. So the struts themselves and upper mounts should be fine.

I'm going on what the mechanic says. He is not a Volvo expert, but has done good work on the car for me so far.

And I already picked up a set of strut housings. ??? So maybe I'll go the route of diagnosis by parts replacement, and have them put in (plus ball joints). An expensive potential fix, but I need to keep the car alive.