If you have to conduct repairs for your Vespa PX125 then it is always a good plan to have access to a Workshop Manual to keep just for reference just in case you want to know ways to strip off a specific component including Drive Shaft and match it again the right way.
Vespa PX125 Workshop Manuals provide you with precise diagnostic info on your vehicle so if something is not working it helps you work out what the situation is and tips to fix it. After that you can analyse if you can do this yourself or if ever the job is too big you can make a booking for your PX125 into a nearby mechanic.
Vespa PX125 manual