If you need to do auto repairs for your PGO TR3 50 then it is usually recommended to have access to a Workshop Manual for reference in case you want to know simple methods to take off a particular component including Gearbox and fit it again in the correct manner.
PGO TR3 50 Workshop Manuals are able to offer precise diagnostic guides for your car therefore if something is playing up it can help you discover what the problem is and the way to resolve it. After that you can assess if this can be done by yourself or if the job is too big you can actually make a booking for your TR3 50 into a decent mechanic.
PGO TR3 50 manual