Depends on age and wear of the disks. Inspection is best to make the decision.

If the original disks and over 10+ years, consideration to replace should be given as for all old rubber components.

The front flex is subject to greater heat and flex than the rear so is more likely to fail.

The consensus seems to be that the disks can be replaced independently unless you are going to remove the entire tail shaft to renew the support bearing in which case both disks should be replaced to save labor.