If you need to perform maintenance tasks on your own Suzuki GN 400 L then it is usually a good idea to own a Workshop Manual for reference just in case you need to know tips to remove a particular component for example Wheel Bearing and match it again properly.
Suzuki GN 400 L Workshop Manuals provides certain diagnostic wisdom with regards to your vehicle so if something is broken it will help you find out what the issue is and the way to make it better. Then you are able to analyse if this can be done by yourself or in case the job is just too big it is possible to make a booking for your GN 400 L into a suitable garage.
Suzuki GN 400 L manual