If you choose to perform maintenance on your Aprilia ETX 125 then it is always a good plan to have a Workshop Manual to keep just for reference should you want to know tips to strip off a specific component much like the Gearbox and fit it again in the right way.
Aprilia ETX 125 Workshop Manuals are able to offer specific diagnostic info for the car or truck therefore if something is broken it will help you find out what the problem is and how to correct it. You can then determine if this can be achieved yourself or in the event the job is just too big it is possible to book your ETX 125 into a decent friendly mechanic.
Aprilia ETX 125 manual