I have a rattling sound coming from just behind the passenger side rear seat of my 96 850 Turbo Wagon. The car has 100K miles on it so it wouldn't be unreasonable for the shock to be gone but based on the posts I've seen on this website it seems to me that the most likely explanation for the rattle is that the mount for the rear shock is gone. Is there a way to definitively tell if the mount is gone or if it is the shock? Assuming that the mount is gone can anyone give a novice mechanic an overview of the steps necessary to replace this and advise on where to get the part and whether I should replace the mount for the other rear shock as well?

As always thanks for your help. These tips save me a lot of labor $$$ when I can do it myself.