If you have to conduct fixes on your Sherco ST 125 then it is always a good idea to possess a Workshop Manual for a reference in the event that you need to know techniques to strip off a specific component like the Brake Discs and fit it again accurately.
Sherco ST 125 Workshop Manuals gives you targeted diagnostic info for your vehicle so if something is wrong it will help you figure out what the problem is and some ways to repair it. You will be able to assess if this can be achieved by yourself or that the job is simply too big you could book your ST 125 into a nearby car garage.
Sherco ST 125 manual