A friend an I owned a motorcycle shop in the 60's. We sold Kawasaki and Maico. We sold a Maico to one guy and after a while he brought it back to the shop in a basket. Somehow he ran the gearbox out of oil and toasted it. He bought all new parts but couldn't figure out how to put it all back together again.
Since we had been selling them for less than a year, I had never been inside one. We didn't even have a factory shop manual. With a little luck and a lot of patience I got it back together again and it worked flawlessly. ...and not a single part left over! It was fun figuring out where all the bearings, snap rings etc each belonged.