I had similar problem with WT10340. Unused new one opened a couple years later after it was received as a gift. Erase was not working at all from the beginning.
I believe that the major problem is that display terminals are loosing contact from PCB after some time. So you should pinch at the point of that contact. There are also two screws around each of those contacts (they should arrange proper pressure at contacts, however this does not seem to work for longer time...) So the best point to pinch is in the middle betwee each couple of screws.
This solution will probably work for some time until those contacts get loose again. Then you will need to pinch again.
If this does not work for you, remove screws, open the cover from electronics and pinch directly on PCB (through those rubber pads). Optionally check the battery, if the problem is not there.