If you choose to carry out auto repairs on your own Kreidler Mustang 125 then it is usually recommended to have a Workshop Manual for a reference should you need to know how you can strip off a certain component for example the Brake Discs and install it again properly.
Kreidler Mustang 125 Workshop Manuals can offer you particular diagnostic information on your car so if something is wrong it helps you understand what the problem is and some ways to fix it. You can then evaluate if this can be done by yourself or if the job is just too big you can actually make a reservation for your Mustang 125 in with a local repair garage.
Kreidler Mustang 125 manual