Here I do an in-depth inspection of the Illinois Bunn Special pocket watch while pre-cleaning the movement, and find several additional faults. Correcting them is necessary to restore the watch to proper working condition.
As with oiling, no two watchmakers clean movements exactly alike. Things get especially confusing when we talk about pre-cleaning: getting major dirt and oil deposits off before final cleaning. Some keep the whole movement together, while others disassemble it beforehand. Some watchmakers use two cleaning machines - one for pre-cleaning, and one for final cleaning. Some do pre-cleaning dry, while others clean parts by hand in alcohol or naptha.
My takeaway is that there is no hard and fast rule, and it depends on how dirty parts affect
a) your ability to find faults, b) the lifespan of your final cleaning fluid, and c) whether you will be able to get the part clean without pre-cleaning. If you do things differently, please chime in! I want to hear how you were taught, and whether your practice has changed over time.