ok I just got home to look up close in photoshop on super zoom. The location of that crack is not from resizing, that looks to me like a bad spot in the casting, like a porousity issue. And that causes a weakness in the ring itself that with the right whack or any pressure will just set it into motion. Because of the size of it and location, it's going to be VERY hard to fix, IF it can be fixed. It would have to be laser welded. But that's pretty big, in that it starts under the basket/stone, and seems to spread upwards into the prong, and that's only going to get worse. The best bet is to have the original owner (who I assume you bought this from) take this to Tiffanys for repair/remake. Bec if you send it in, and you're not the owner, it will take a while and the seller is going to refund it now. Either they know there's damage/issue, and they priced accordingly, or they didn't and now they're embarrassed. HOPEFULLY if they refund it they don't just relist it and sucker someone into buying a damaged piece,
That is what happened to me with WF and that isn't above any company that does casting, period.
Also mine doens't have a size in it.