Rear end steer is usually the torque and thrust arms. Both run between the wheel carrier and towards the outside of the subframe.
In all, there are five links in the multilink suspension: torque, thrust, camber, tie rod, and lower control arm. The lower control arm is a wide piece that goes between the subframe and the bottom of the wheel carrier. The camber arm goes between the subframe and the top of the wheel carrier. The tie rod is on the front side - the side in the wheel carrier has a ball joint, the side on the subframe is a bushing. The shorter, thicker link is the torque arm which mounts higher than the longer, thinner thrust arm.
Over time the rubber bushings that connect these links pretty much just rots leaving the links loose and causing your torque steer.