If you wish to undertake maintenance tasks on your Vespa S 125 then it is usually recommended to possess a Workshop Manual for personal reference should you need to know the best way to take out a specific component like the Exhaust and fit it again effectively.
Vespa S 125 Workshop Manuals gives you exact diagnostic info on your car or truck so if something is broken it can help you understand what the problem is and ways to resolve it. Then you are able to evaluate if this can be achieved by yourself or if the job is simply too big it is possible to make a reservation for your S 125 in with a trusted car garage.
Vespa S 125 manual