Given that (if I read this correctly) he had two chances of fixing it and couldnt, and seemed to have done something completely unrelated instead (replace the main spring), might it be a good idea to approach Omega with this? Politely tell the story, mention that you've lost your confidence in the abilities of said watchmaker and ask if there is another way, have Omega fix it, for example? I'd assume the service bill might make them cooperative.
I don't know, people make mistakes and all, but since he seems to be overwhelmed by the watch, it might be a good idea to have somebody else fix this. Yes, you know now what the issue is and that'll make it easier for the WM, but I'd be left wondering what else there is he might have done half-heartedly. Am I being too harsh?