I noticed my Silvia is taking to longer to brew, that espresso is coming out with less crema, and that the top of the puck when I pull out the portafilter is very wet, like water is not getting "pushed through" as well. I would summarize it as "decreased pressure."
I regularly clean the unit, and it seems to be fine otherwise. Grind and tamp are the same everyday. Espresso tastes good still, though not as full-bodied.

Coffee Makers & Espresso... - Rancilio - Silvia Espresso Machine