When a watch is serviced, oil is placed at specific areas of wear such as pivot holes. As time goes by, dust enters the watch and the oil deteriorates. This deteriorated oil mixes with the dust and create a sticky gritty substance that actually wears the pivots more than if there was no oil at all . The balance wheel in particular receives extreme wear, as it oscillates from 14,400 to 36,000 times per hour. That is why a watch is oiled very sparingly, reducing the possibility of oil migrating to other parts of the watch and gathering more dust.
In the early century, watchmakers claimed that a watch should be cleaned and oiled every year or year and a half at the most. The oils used at that time did not hold up as well as modern synthetic lubrication. Even at that, many people of the time ignored that advice and many watches were not serviced for five to ten years, or until the watch stopped working.
If you have acquired an old watch that has not been run for quite some time and plan to start using it, then it should be fully serviced. After that it is generally recommended that a watch be serviced every 3-5 years if run on a daily basis. How a watch is serviced may very from watchmaker to watchmaker, but when I service a watch the following procedure is followed:
- Complete disassembly
- Cleaned in a three chemical agitation
- cleaning machine,
- inspected for wear
- re-assembled,and oiled
- mainspring replaced if needed
- Regulated (as apposed to adjusting)
Complete disassembly is generally considered the best way to clean a watch. I use an agitation cleaner, instead of an ultrasonic cleaner because ultrasonic cleaners tend to loosen jewels that have been set with shellac (such as pallet and roller jewels). Also, since the watch is apart already, it makes sense to replace the mainspring (unless it has been recently replaced).