I tried the tooth brush, and it got some of the stuff out, but my fear of getting too much water into the head unit held me back. Then I tried a thick piece of paper, like a heavy card stock, cut it into little strips, applied a tiny bit of 409 to the corner, and while holding the button down squeezed the paper in between the button and the button hole. It seems to have worked. Lots of brown stuff was on the paper once I pulled it out, and I just used a new piece each time. Seems simple, but the buttons are better now!
