For all my B&O, I use glass cleaner (for sunglasses), it usually works great on those aluminum surfaces. I use is for all my Beomasters (including a Beomaster 4400 :), Beograms, Beocords and even Beovox speakers. But just be sure that the type of cleaner you use doesn't remove the lettering and printings on your 3000/4000/4400, I have been using denatured alcohol for my Beomaster 6000, but not sure if the 3000 family printing can handle it.
-Søren
Beocenter 9300, Beogam CD50, Beocord 5500, Beomaster 3400, Beomaster 4400, 2 Beogram 4000, Beomaster 8000, 2 beogram 8002, Beovox S-75, Beovox MS150.2, Beovox RL6000, Beovox S-35, Beomaster 6000, 2 Beocord 9000, Beocord 8004, Beocord 5000, Form 1, 2x Beolink 1000, Beo4, MX3500, LS4500. Born 1993.