If you have to do repairs to your Vespa GT60 then it is usually a good idea to possess a Workshop Manual to keep just for reference in case that you need to know how to take off a specific component such as the Door and install it again accordingly.
Vespa GT60 Workshop Manuals offers clear specific diagnostic guidelines for the vehicle so if something is playing up it can help you work out what the issue is and how to repair it. After that you can evaluate if this can be done yourself or if the job is just too big you can still make a booking for your GT60 in with a trusted friendly mechanic.
Vespa GT60 manual