It’s been said many times on this forum that a watch can look great on a timegrapher, but still need a service. So, to put it a different way: are there one or more of the parameters that are typically displayed on these devices that tip off experienced watch repairers that there’s a need for an overall service, rather than a non-service related, and perhaps isolated issue?
IMO there's no substitute for a visual inspection with high magnification, even if the timing results look good.
You sound like the urologist. PSA test not good enough. Me: “Where should I put my pants, Doc?” Doc: “Put them on that chair, next to my pants”
My friend, Paul Sheehan, once told me years ago: “Bob, there is no such thing as a gay Irishman; they become urologists...”
Low amplitude. Large positional variations. Lack of isochronism. Wavy lines. But then it wouldn't look good on a timegrapher.
Low amplitude and high beat error is the biggest tell I would say, accuracy can be good even with amplitude being low and newbies often focus solely on accuracy.
Low amplitude is a good tell tale for the need for service, if all else looks fine (e.g. beat error, etc).