As a follow-up, my Seamaster arrived home today. I'm very happy with the service, but, honestly, I'm not
completely sure I'd do the same again. The logistics turned out to be a little stressful. I certainly defer to Rob's expertise in avoiding issues with Thai customs, and I appreciate his efforts to minimize the shipping costs for his customers, but the somewhat complicated process—with intermediaries in both directions—seems to introduce plenty of opportunities for things to go wrong.
I followed Rob's detailed shipping instructions exactly, though my local post office wouldn't accept his forms. They asked me to transfer all the information to paper forms they provided for ease of automatic scanning. In any case, I handed the watch over to USPS on 21 January. Rob received the watch on 18 February. For the return trip, DHL picked up the watch on 2 June, and USPS delivered it to my mailbox today (18 June). Possibly I'm spoiled by purchasing watches from Japan, Singapore, etc. and having them in my hands two or three days later, but 46 calendar days in transit seems like quite a lot. Also possibly I'm overly paranoid. I don't worry about watches when they're in the possession of a watchmaker, but my imagination does tend to get a bit overactive when thinking about what a mail carrier or commercial shipper might do.
Ultimately, though, all's well that ends well. The watch is in fabulous shape, the costs were more than reasonable, and a 5-month wait isn't too bad overall. I've had watches in service with Omega for more than twice that long.