Check the headphone jack. There's a mechanical (springy metal bit) switch inside the jack that signals to disable the speaker when the headphone is plugged in. Most likely, that springy metal isn't springing any more and is leaving the speaker permanently disconnected. If you can hunt up a schematic, you can probably identify a couple of pins on the jack that you could short to see if that reenables the speaker. Might also be in "The Dead Mac Scrolls".