Col,
Personally, I run my Rolex until it stops or begins running erratically. Obviously, we would never do that with an automobile, but there are reasons why I would recommend this.
First, we've been using synthetic oil in timepieces since the early-1960s. I've been told that synthetic oil will run for an unlimited term, if not contaminated.
Previous to that, we ran natural oil of some type (sperm whale or mineral) and they eventually deposited a form of shellac on the jewels. My father became an apprentice watchmaker in 1929 and at that time it was recommended to "clean" a watch every year. The organically-based oil broke down in one to two years use and the watch needed to be both washed in a cleaning solution and the oil replaced. Some of the cleaning agents caused leukemia ... guess what my Dad died from???
The synthetic oil does not break down unless it is either contaminated with water or "junk" (skin dander, fuzz ... you would not believe the stuff I have seen in watches
). If the watch is well sealed; tight crystal, good back gasket and a well-fitting crown gasket, you can get lots and lots of years out of a service.
The most powerful of watch mainsprings create less than one-millionth of a horsepower, so when the oil is dicked (a technical term
), the watch will stop. Or if the oil increases viscosity, from certain types of contamination, it will get into the mainspring. This effectively shortens the mainspring and the watch will run many hours fast every day.
In sum, if the watch has been well serviced, simply run it until it is no longer running well. Then, have it serviced by a good shop.
Note, if you get a crack in the crystal, or the crystal fogs up (indicating a leak somewhere), RUN DON'T WALK to a good watch repairman and have the source of the leak fixed. As I said, it can be any of the three; crystal, crown gasket or back gasket.
A tightly-sealed watch in good order should run ten to fifteen years between servicings. My Rolex has not been touched for well over twenty years and it is still running very well.
Hope this helps.
God Bless,
Steve