The brass dust is most likely coming from the left flipper plunger stop. There is a brass part in it that eventually wears completely out, and then the flipper starts getting stuck in the upright position. No need to worry, pretty standard wear item for newer sterns. Maybe just order a spare and have it on hand for when the flipper starts sticking.
As far as the squeaking goes, good luck. Sometimes you can stop it, sometimes not.