If you need to carry out fixes on your Vespa ET 4 then it will always be a great idea to have a Workshop Manual for reference in case that you need to know the best ways to take out a particular part including Exhaust and install it again safely.
Vespa ET 4 Workshop Manuals provides particular diagnostic guidelines for your vehicle therefore if something is faulty it will help you identify what the problem is and tips on how to fix it. After that you can determine if this can be done on your own or if the job is just too big it is possible to make a reservation for your ET 4 in with a suitable friendly mechanic.
Vespa ET 4 manual