Sach is a good bike, But the trans do have a flaw in them. The flaw is the drive gear is press fit on the shaft. So when a Sach has a trans problem, drive gear has slipped and needs to be replaced. If you do find a new one take it to a weld shop and tack the gear on part.
If it cheap it worth monkey'en on. You find by looking at profiles. That people tend to 1 or 2 bands.There are some moped heads who have everything