Hm... there is (low-volume) sound with headphones. And now that I listen for it, there is some barely-audible sound coming out of the speaker if the volume's all the way up, though I'm not sure whether it was always there or if it's just a result of all the extra cleaning and component swapping I did today.

The dishwasher thing is intriguing; I've never heard of such a thing before. However, we don't have one, so that's not an option.

I did notice a little bit of oxidation where Q1 and Q2 are joined to the logic board on the edge of the no-sound board (though I guess that should be the "faint-sound" board now). That board overall was a little dusty (I've cleaned it up as well as I can), but that was the only point at which I noticed any oxidation.

The pinstripes board looks pristine.