I've had at least one drive fail that worked when I cleaned those pads. I often take the PCB off drives and those pads tarnish something awful. I'm guessing they're silver-plated (the tarnish coloration looks like silver does) and usually the pogo pins on mechanism make a gas-tight weld. I take an eraser and clean them all shiny and wipe the pogo pins before I reassemble, for good measure.