If you choose to do fixes for your MBK Nitro then it will always be a good idea to possess a Workshop Manual to keep just for a guide in case you need to know simple methods to take out a particular component such as the Gearbox and install it again appropriately.
MBK Nitro Workshop Manuals are able to offer specific diagnostic details for your car so if something is playing up it will help you understand what the issue is and how you can correct it. After that you can decide if you can do this yourself or if ever the job is simply too big you can actually make a booking for your Nitro into a decent garage.
MBK Nitro manual