If you wish to execute adjustments on your PGO BuBu 125 then it is usually a great idea to own a Workshop Manual to use as a reference in case you need to know proven methods to take off a certain part such as the Gearbox and fit it again correctly.
PGO BuBu 125 Workshop Manuals gives you unique diagnostic guides on your vehicle therefore if something is broken it helps you understand what the situation is and ways to repair it. After that you can determine if you can do this by yourself or if ever the job is too big you can book your BuBu 125 into a local car garage.
PGO BuBu 125 manual