If you need to perform repairs for your BMW R1200GS then it is always recommended to own a Workshop Manual to use as reference should you want to know the best way to take out a particular component for example Brake Discs and match it again properly.
BMW R1200GS Workshop Manuals are able to offer distinct diagnostic guides for the car therefore if something is not working it will help you find out what the issue is and how you can correct it. You will be able to assess if this can be done on your own or in case the job is too big you can actually make a reservation for your R1200GS into a local garage.
BMW R1200GS manual