Originally Posted by Mister Moo

A grouphead gasket that has begun to leak has already lost its elasticity; in other words, through continued heat and compression the thing has gone just about rock hard. To spare yourself the inevitable unpleasant gouging out of a failed, glued-in grouphead gasket, change them once a year while they are still pliable and still easy to remove.

O-rings, associated with steam wand seals, are best changed before they begin to leak, too. I say, be a big shot and spring for the $0.65 early. Change the o-ring when you replace the grouphead gasket.