How are your soldering skills?
Take any AC to DC power supply, the thicker the wires the better, and split the 2 wires, solder on an alligator clip to one wire and a wire hanger on the other.
Get a small, useless glass, and fashion a circle out of the wire hanger to fit in the bottom of the glass, solder the other wire to the other end of the hanger, and VOILA!!! You have a electronic jewelry / coin cleaner. You'll be able to see the bubbles coming from the alligator clip end.
If the date is totally gone, you might have to resort to sulfuric acid to
get anything to show up at all.