I've sold pipes internationally on eBay for about 5 years. I have dealt a number of times with 2nd party shippers too. That's a nice option that eliminates any worry on my part.
I haven't kept track, but I'd guess I've sent 30-50 pipes to other countries directly. I have a disclaimer in my descriptions that, excepting Canada, only Priority Express has a tracking option. I leave it up to the buyer. They always choose the lowest price option. I send them the US Customs number as proof of mailing.
Occasionally a person won't understand the disclaimer and ask for tracking info. I try and be patient and explain it to them. But those instances make me a bit nervous.
On the good side though, I have never lost a package. Or at least I've never had a claim filed against me. I've mailed pipes to Russia, China, Japan, Hungary, the UK, Brazil and others I'm probably forgetting. Probably more to China than anywhere else.
If your watch is really valuable, I'd select only the Express Priority with insurance option so it can be tracked. That may discourage some buyers as it would be expensive. But it would definitely be better for your piece of mind. An overseas collector with deep pockets won't care.