Cleaning and oiling the movement
Now that the watch and movement disassembled it’s time to clean it. Each part of the movement and the watch case are cleaned thoroughly in either an ultra sonic cleaner, or a naptha solution may be used. If you choose to use naptha, please be very careful, this chemical is toxic and can harm you if not used properly. Once the parts are cleaned, allow them to dry on a lint free cloth or paper towel. Any lint or dust you introduce to the movement at this point will defeat the purpose of cleaning it.
Once all of the watch parts are cleaned it is time to oil. When oiling a movement there is a very fine balance between using enough oil to provide lubrication and using too much oil and having it attract dust and creating a mess inside the watch. Very little oil is actually needed since only very small drops are placed on each jewel or pivot hole. One area you want to avoid getting oil on is the hairspring. The oil will cause the spring coils to stick to each other and keep the watch from functioning properly.
Reassembling the watch
Now that the movement has been properly cleaned and oiled its time to put the watch movement back together. The process is simply the reverse of disassembly. However, extreme care needs to be taken. Each gear should easily slide in to place and the screws that hold them should tighten easily. Any binding or tightness needs to be address immediately or the watch will most likely not function properly.
Once the movement is reassembled we can replace the dial and the hands and then place the movement back in to the cleaned watch case.
As you can see, there is a lot that goes in to servicing a watch and a lot that can affect the time and skill required. I am very comfortable taking apart a simple mechanical watch, but as the complexity of design increases I become less and less confident. Even after taking watch repair classes from people like Dan Gendron, now retired, I find myself looking in to these watches and marveling at the complexity.