Scott
Thanks for your interest...
I have a range of watches, from a 1970s Rado through to a G-Shock. All bar a couple have been bought 2nd hand and I have them serviced when required by an independent. As you say there could be many reasons for the movement 'failing' but it is also the movement in the JLC - Master Compressor World TImer so should be robust given that watch's 'advertising' but the Amvox does not have the shock absorbing elements of the case.
If it was older stock in the AD then I'm sure they will come back and tell me but I would have expected the AD to let me know at the time that the watch would need servicing before the standard 3-5 year window.
I'm still waiting for Customer Services to get back to me with their view so there is still some 'hope.'