Most Italian families don't usually clean their moka beyond a quick rinse - it's normal to have a thin brown patina in the top chamber. It quickly reaches an equilibrium and stops accumulating, and the same goes for the filter and gasket. In fact, many will throw out the first brew or two when getting a new one or after monthly-ish cleaning.
I guess it may sound icky at first, but in practice it mostly stops the coffee from direct metal contact.