I bought a similar box with the typical left speaker not working in stereo mode. The bass and treble sliders didn't work at all as well. Additionally, the unit didn't work with batteries. I sprayed all the contacts associated with the battery module and cleaned all the sliders with deoxit. Now I'm getting sound out of the left speaker in stereo and the unit works with batteries. Additionally the bass and treble sliders are working, but if the bass slider is at '0' position, the left speaker doesn't work. Strange. But who wants to use a radio with 0 bass?!? Nonetheless, the sliders may be on their way out, so i'm not going to leave them be ;)
I'm happy that I was able to get the box in a condition deemed adequate, as this box is one of my more aesthetically minty examples.