The crystal has come loose at the bottom…
Looking from the side, you can see how the crystal is lifted up a bit at the right.
And here is the culprit. A metal bar with threads is soldered to a copper layer on the crystal, and the soldering joint has broken. I would love to re-solder the joint, but that would almost certainly damaged the inner coating of the crystal and show up. So I decide to choose a different weapon here and trundle off to B&Q to buy some Evo-Stick Metal two component glue. It’s made for metal joints (solder in this case), and is an epoxy two component glue, so probably the right stuff for something like this.
I clean both sides of the joint under the microscope, to make sure all traces of dirt are gone.
When mixing the epoxy, you have to make sure you have exactly the same amount of the two components. I use micro scales to measure the amounts. Once properly mixed (this is important), you have less than three minutes to apply…
Once properly in position, I put a watchmaker’s vise on top of the metal bar and leave it there for an hour. Even though the glue claims to set in 5 minutes, I will give it a lot more time.
After a hour, I take the vise off, and now will let the glue set for another 12 hours.
It’s the next morning, and I can put the crystal back on.
The crystal now sits perfectly flat on the case, and the watch is ready to be shipped back.