So I am about to send a watch (still in warranty) to Sinn Germany and have the labels and everything, but I have been reading up a little online and I was wondering if anyone has any experience in doing so and what paperwork (beyond a photocopy of the warranty card) I need to have in the package (and exactly where they can be obtained, I am not sure where to get the appropriate customs forms). I've also heard an invoice should be included, but I only recently received the watch (it was originally purchased at Sinn Spezialuhren itself and it is not a watch that can be serviced/repaired in the US anyways) so I didn't know if anyone has any advice on how to proceed.
I also was wondering (in regards to future reference), how best to go about sending an out-of-warranty watch to Sinn (specifically a 156B). What paperwork should be included to avoid getting hit with customs?
Any other tips people have who have sent their watches back to the motherland? I'm relatively new to watches (have not really had things serviced much nor any 'go to' watchmakers) so it is a little more nerve-wracking having to send it all the way across the pond so any and all advice is much appreciated!