Not sure if this is going to help you or not, but I'm going to post it anyways..
Ok, before I got my new struts and mounts, the town fair tire could not get the caster into spec.
They said there is no caster adjustment and that the mounts are shot and causing it.
Looked like this:
When I saw my front mounts they removed from the car, I understood why they could not get them into spec..
After new struts and mounts they were able to get it into spec:
You sure your looking at a rear caster problem?? I don't even see rear caster as a spec..
Anyways.. Good luck, hope my pics help and you get it sorted out.