In 200,000 miles, I have gone through three sets of rear shock mounts due to failure of the mounts.

So, I would say, replace them as they are, in my opinion, not a 200,000 mile item.

Something I remember from when I first replaced them . . . for probably an assembly reason, Volvo used extra long bolts to hold the mounts to the body, with all of the several inches of extra thread sitting out there, exposed to the elements for years. It took a lot of time and a lot of WD40 to remove those bolts and, when I did, I cut them short so the next time I had to do the job it was quite a bit easier.