The frequency of service can depend on many contributing factors. The main influences are environmental. Heating, air conditioning and circulating air will eventually have a drying (thickening) effect on the lubricants used in your precision timepiece. In addition, microscopic particles of dust, dirt and other foreign matter will settle inside and on the mechanism. These particles mix with the lubricant and over time also contribute to the thickening process, eventually leading to a gummy or tar like substance in and around the bushings or bearings. You may begin to notice a gradual slowing of the ¼ hour chiming and⁄or the hourly strike due to the increase of “drag”. This progressive condition will lead to excessive wear on the “bushing”. The bushing is made of brass and the “pivot” (the shaft portion of the wheel that turns in the bushing) is made of steel. When you combine the dirt, thickened oil, and the action of the pivot rotating, you have an abrasive condition which, over time, causes catastrophic wear to the bushing. Inevitably, the wheel–to–pinion indexing will be affected and lead to a lock–up of the “gear train”.
Your clock is a mechanical and precision instrument, therefore, is vulnerable to wear and breakdown. Routine maintenance is required to ensure smooth, uninterrupted performance. Traditionally, it was suggested that clocks be lubricated about once a year. That was true when lesser quality animal based and petroleum lubricates were used. However today, synthetic lubricates have emerged and are far more superior to those in the past. Therefore, the recommended frequency of routine maintenance has decreased (see below). I only use lubricates recommended by the leading manufactures. Be aware, some repair technicians still use lesser quality oils because their cost is a fraction of the synthetics used by most manufactures.