If you wish to undertake maintenance on your Yamaha DT 125 RE then it will always be a great idea to possess a Workshop Manual to use as personal reference in the event that you want to know simple methods to remove a certain component much like the Brake Discs and fit it again successfully.
Yamaha DT 125 RE Workshop Manuals gives you specified diagnostic wisdom for the car so if something is faulty it helps you work out what the issue is and tips on how to make it better. You will be able to analyse if you can do this yourself or in case the job is too big you can actually make a reservation for your DT 125 RE in to a nearby car garage.
Yamaha DT 125 RE manual