Someone mentioned before on this thread that it's common for Electrolytic and Tantalum capacitors to have opposite polarity markings, are we *absolutely positive* that doesn't explain the confusion here?

I *seriously* doubt these machines shipped with an electrolytic capacitor that was put in backwards. Electrolytics have this nasty habit of blowing up like bombs when run in reverse (seen it in the flesh several times), and even if by some miracle that didn't happen it'd still heat up and act like a (partially) shorted circuit. This is the sort of thing the manufacturer would have noticed after shipping a few thousand units.