The brew group on an espresso machine is an unusually harsh environment.  Temperature is constantly changing, coffee debris and limescale collect and the crushing action of the portafilter handle as it is locked in place also raises havoc on the rubber group gasket. They get hard and brittle; and eventually loose their ability to seal against the filter basket and worse, will destroy the soft brass edges of your expensive portafilters so you will get water jets when you go to make a shot. After six months these gaskets should be replaced - sooner if you keep your machine on 24x7.  Call us!!