I call BS!
of course, our resident watchmaker will address this better than I ever could, but if your mainspring is still in working condition, the watch was properly serviced + reassembled + regulated… then it should work properly.
At least this is what happened with my 2998-4: working great (within +/- 5 sec / day or better, nearly 320 degree of amplitude) and passed water test… even if I am not taking it in the pool/ocean.
Edit: and IF a part/parts are too worn, are no longer available (NLA) and do affect time-keeping, then I would expect the watchmaker servicing the watch to let me know what is going on before sending the watch back.
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