If you want to execute maintenance tasks to your Ducati 900 SL Superlight then it will always be a great idea to have access to a Workshop Manual to keep just for reference if perhaps you need to know methods to take out a particular component including Gearbox and install it again successfully.
Ducati 900 SL Superlight Workshop Manuals can provide detailed diagnostic details on your vehicle so if something is not working it can help you identify what the situation is and the best way to repair it. You can then evaluate if this can be achieved by yourself or that the job is too big you can actually make a reservation for your 900 SL Superlight into a decent repair garage.
Ducati 900 SL Superlight manual