I have a large number of those crystals here too. Very few of them work. I opened a few dead ones to see what was wrong with them with a view to fixing them if I could.

All of them had at least one of the small wires that were plated onto the crystal corroded into two pieces.

Somehow moisture had gotten into the case and rusted the wire through.

To me, they are unrepairable. Even the empty cases have almost no use.

If they don't show any activity, the best thing to do is to simply toss them all.

Ken W7EKB