On bikes that are 20+ years old I tend to replace the seals once ive disturbed them. Often they can be resued with a clean up, providing they havent swelled up and fit properly in the recesses.

If you knick them then they are not so good

For peace of mind I repalce them, however, every year or there about I remove the pistons and give the brakes a good clean up and resuse the seals for upto 5 years providing no dirt or shit has ruined them.

Never had a problem.