Not really. I keep all of the parts covered, and thoroughly clean the work surface before I reassemble the watches. There isn't usually any time between cleaning and reassembly. Once everything has been dried, it is put into covered parts bins and assembly begins right then. I do my best to avoid any contamination, and the microscope really helps a lot. Thus far I'm getting pretty good results, at least my timegrapher thinks so! The parts only come out of the covered bins when it is time to install them, and everything is doublechecked with the optic during assembly.
