If you wish to conduct repairs to your Yamaha RD 400 then it will always be a good idea to have a Workshop Manual to use as reference in case that you need to know easy methods to take out a particular component for example the Door and install it again in the correct way.
Yamaha RD 400 Workshop Manuals can provide precise diagnostic guidelines for the car or truck so if something is wrong it helps you identify what the issue is and how to repair it. You can then evaluate if you can do this by yourself or in the event the job is simply too big you can actually make a reservation for your RD 400 in to a decent repair garage.
Yamaha RD 400 manual