I'ved heard from accounts in WUS forums where the watch can be keeping time but the insides are grinding against each other and wearing out. ETA ok but in-house parts replacements may be more costly. I'd say send for servicing between 5 to 7 years? of course if one dives then the gaskets need to be checked more often. Thats all not from personal experience but from others.
hard to discuss on here especially since there's no science or hard data to back this up. consider the folowing:
- many daily beater seikos go along just fine for 10-20 years without scheduled servicing. if it does usually its a common part that is designed to fail, seldom a totally lost cause.
- synthetic oils of today don't just dry up or expire after 5 years with no trace in a sealed sterile environment (from factory). this is no car engine, no extreme temps to deal with and no contaminants to constantly clean. its a precisely engineered instrument.
- synthetic oils of today are excellent. as are material purity and engineering specs and tolerances.
- servicing won't detect many problems if the watch is still within specs, manufacturers still can't explain failures for regularly serviced watches
- even more so for local service centres who seem to be efficiency oriented. even profit motivated. don't get me wrong - if i lived in europe i'd glad let them take my money for regular servicing.
the point about the high costs of low-supply parts is just something you have to accept; kinda like owning a ferrari requiring a costly clutch change every 10k KM or so.
however i do track my watches to ensure that they are within specs - variance of up to 25sec a day for two days - going so far as to sync it to the second against my PC or smartphone time. once the timing is off, time for a visit. its something i enjoy doing though...for others i can see why just sending it to the service centre provides peace of mind.