The seals may well swell with age, but also the recesses that the seals sit in get crap deposited in them so the seals stick out more than they should. This makes the fit too tight and stops the pistons going back in.

You need to clean out those recesses, and really get new seals, for the sake of a few quid it's madness to not replace them whilst you've got the calipers apart.

Also, give the pistons a good rub with fine wet/dry or wire-wool to get rid of any deposits/corrosion.

Do this and they will work like new.

Good luck.

Al.
_________________
Cheers....

Al

Bikes:
GPZ900
NC30
NSR250SE
RGV250 vj22