I've never seen worn trailing arm bushings on an 850 to date. What I do see, the main reason for incorrect rear camber is bent trailing arms and that can usually be seen if one carefully looks at them from under the car. When they're bent (reason not known to me, accident, etc?) they must be replaced and they're not cheap.
Either way, bent arms or worn bushings, your car will then need a 4 wheel alignment to get the rear toe in specs afterwords.