Common advice says service every five years, but service is expensive and some people run watches much longer. What observable signs actually indicate a mechanical watch needs attention, as opposed to just being due on a calendar?
Discussion record: RWF-14441.
The calendar interval is a conservative default, not a rule. Useful signs, in rough order of seriousness: power reserve noticeably shorter than spec from full wind, rate drifting outside its usual range, the watch stopping on the wrist, gritty or rough winding, and the date changing slowly or late.
Clarifying question first: do you have a baseline? If you've never recorded the watch's rate or power reserve, 'drifting' is hard to judge. Start a simple log now with daily offset against a reference time for a week, and the hours it runs from full wind. Once you have that, later changes mean something.
If the manufacturer provides a suitable procedure, a running-time log can support a service enquiry. State the winding method and stop time. A shortened run does not identify the cause by itself.
A sudden rate change has several possible causes. Ask a watchmaker to test suspected magnetism rather than diagnosing it from a compass or attempting an adjustment based on forum replies.
Sealing and movement performance are separate questions. Ask a qualified watchmaker about inspection and testing appropriate to the particular watch and its intended use; a healthy rate does not establish water resistance.
Keep a baseline log, describe changes in rate or running time and stop forcing rough winding. Follow the manufacturer’s guidance and arrange professional assessment when operation changes. A forum cannot prescribe a universal service interval.
Clarification for “Maintenance question: how do I tell if an automatic actually needs service?”: the point beginning “The calendar interval is a conservative…” belongs to the question as written. It should not be read as a report that a new check, purchase or experiment has been completed. Review focus: scope. Keep the stated question separate from any broader claim.
Method note for “Maintenance question: how do I tell if an automatic actually needs service?”: use “The calendar interval is a conservative…” as a row heading in a proposed working record. Put the statement, its supporting source or measurement, and any unresolved detail in separate fields. This proposes a format; it supplies no additional evidence. Keep the stated question separate from any broader claim.