If you choose to do auto repairs to your Vespa GT Navy 125 then it will always be recommended to have a Workshop Manual for personal reference if perhaps you want to know the best way to take out a specific component like the Brake Discs and match it again safely.
Vespa GT Navy 125 Workshop Manuals gives you specific diagnostic details with regards to your vehicle so if something is wrong it can help you identify what the situation is and the best way to resolve it. You will be able to assess if this can be done by yourself or in the event the job is too big you can actually make a booking for your GT Navy 125 in to a suitable repair garage.
Vespa GT Navy 125 manual