For what it takes to repair it,,, you need to do both sides, and replace the sway bar bushings..
Likely the bushing at top of reat strut mounting is blown out (they used compressed foam, and it rots, and the struts crash around.. reach in the wheel well, find the top of the strut shaft... there is a washer you can feel, feel around it and see if the washer is real close to the steel mounting, and if you can feel shredded foam mashed out.
The first 2 pics show where you will be feeling for foam blown out... this example has the newer rubber bushings installed.
This pic shows the upper arm pivot points.. make sure only movement is on the pivot point.. if the arm flops around loosely, then either the arm,, mounting, or both need replacement... order new bolts and stuff too.
You will want to replace both strut, all the upper mounting rubber, 2 sleeves, nuts, washers, and steel plates that the shock boots fit over..
Also grab the upper control arm, and make sure it is sure, only movement it should have is on the pivot point... had 1 come in recently that the mount was broken, arm knocking around...
Depending on where you at, frame recall on front for rust eat through and arm pulls off frame... done a pile of frame replacement