If you choose to execute fixes to your Suzuki GN 400 L then it will always be recommended to own a Workshop Manual to use as reference in the event that you need to know tips on how to strip off a particular part including Door and match it again properly.
Suzuki GN 400 L Workshop Manuals provide you with specified diagnostic facts with regards to your car so if something is playing up it will help you ascertain what the problem is and tips on how to make it better. You will be able to assess if this can be done by yourself or in the event the job is just too big you can still make a reservation for your GN 400 L into a suitable car garage.
Suzuki GN 400 L manual