Thanks,
15 minutes of work and i have now a very clean unit.
I didn't use my car, was a nice walk !! :-*
Are you speaking about the clear plastic casing ? if so, was pretty dull as well, so removed the rear foot (3 small Allen screws) then the 4 screws of the rear casing and proceed to clean it...inside and out.
15 minutes of work and i have now a very clean unit.