There's nothing particularly difficult about the Leica mechanics; as you found, they come apart and go back together relatively easily, as long as you pay attention to all the little parts and how they fit. There are, however, a few points to note. One is that there are adjustments that can be very fiddly to get exactly right (slow speed lever, shutter brake on the later models, curtain tension, to name a few). The second is the question of lubrication; Leica used a ridiculous number of different lubricants in these cameras, and while I've never tried to determine the properties of each, let alone replicate them (whale oil is hard to find these days), careful lubrication is important to maximize the life of the components. I've found that Breakfree CLP (a firearms lubricant) is a good general purpose oil, while molybdenum grease, clear synthetic all-purpose grease (Superlube), and synthetic automotive wheel bearing grease are useful in different areas.
