If you have to perform maintenance on your own Derbi Boulevard 125 4T then it is usually a great idea to own a Workshop Manual to use as a reference in the event that you need to know proven methods to take off a particular component much like the Drive Shaft and fit it again in the right way.
Derbi Boulevard 125 4T Workshop Manuals will give you unique diagnostic info on your car or truck therefore if something is wrong it will help you work out what the situation is and tips to fix it. After that you can determine if you can do this by yourself or if ever the job is simply too big you are able to book your Boulevard 125 4T right into a trusted mechanic.
Derbi Boulevard 125 4T manual