1. Yes, all mechanical watches need to be serviced periodically (4-6 years)
as the lubricant will dry up over time.
Sorry, but you are wrong.
Modern lubricants do not dry up any longer.
And they have not done so for many many years,
because those lubricants exsit for decades already.
Some experts say:
"You just wait until that movement starts to be slow or stops."
And others:
"Ten to 15 years between services will do."
2. Costs of servicing a watch varies from brand to brand but 10% sound close.
Service costs depend on in which country you live ... and also:
what watchmaker and what kind of movement?
Over here, in Germany, it is about $90 US.
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As to Baume et Mercier and Maurice Lacroix:
Both excellent Swiss watches, though not very known (and bought) in Europe.
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"Tag Heuer" ?
Great watches of excellent and
highest quality!! ... just to dream of! ....
Regards,
BBouvier