Hi Al,
Thank you for the feedback.
It turns out the local jeweler sent the watch to a watchmaker in Plymouth Michigan called "On Time Watch Experts."
https://ontimewatchexperts.com/
I just got off the phone with the watchmaker. He says he has 35 years experience and does in fact have a parts account with Omega (as well as Rolex).
He says the actual problem isn't that the mainplate is
broken. Rather, he says there is a screw in the mainplate that "holds a bridge" that sheered off, leaving a piece of the broken screw in the mainplate. He said that although it might take him a couple of hours, he could remove the broken screw and replace it with a new one. He says that if we send it to Omega, in all likelihood they will simply replace the mainplate and it will end up costing more than the $1,700 he quoted.
Would an unattached bridge cause the rattling in a watch that otherwise seems to work?
I told him that I want a second opinion from Omega, and he said that was fine.
Assuming this updated description makes sense, what would you do?