UR20Z
Dumpster Diver
For future reference: If ever you have opal in a setting, *AT LEAST* once a month, take it off and let it sit overnight in a glass of water (distilled best, but as long as it's not super-hard or nasty with iron, it'll do)
Opals will and DO dry up, and in the process, shrink somewhat - all-too-often, enough that they can fall out of the setting.
The simple fix is, as noted, soak 'em at least once a month.