This subject was buried in the Changing Your Oil topic so I thought I'd give it a topic all of its own as a lot of people (including myself) had no idea that you had to add & change your transmission oil. Here's how it's done on my Taishan Commuter and it should be pretty much the same on all Chinese scooters:
Near the back wheel look for a nut with a washer which will look a bit different to all the rest:
(As you can see the top is completely flat whereas all the others aren't)
Undo the nut and pour some oil in, because the hole is so small it will be tricky. I just held the nozzle tight to the hole and squeezed the bottle, it seemed to go in.
Look under the nut and you'll see a draining bolt:
You undo this when you want to drain your transmission oil.
There is a special transmission oil that you can buy but if you want you can just use your normal 10w/40 oil that you use for the engine.
Do not use oil for automatic transmissions! Use transmission oil for manual gears. Also, I would not recommend to use the same oil for the transmission as for the engine. It will work, but is not very good.
Automatic transmission fluid does what it says on the can! it is a type of hydraulic fluid( some car braking systems actually use it) for auto gearbox's and is not suitable for the final drive on these scooters may even damage the oil seals. Auto gearboxes are hydraullicly operated. You should use gear oil which is designed for the forces etc in meshing gears ep80 probably ok. I think there is some fairly low viscosity oil for scooter gearboxs at Halfords
Its even easier if you get a large syringe, I use a 60ml, avaliable from chemists or car shops, and a piece of fish tank tubing (for air pumps etc) pushed on to the end. If its too tight put the end of the tube in hot water to soften it. I find this is the perfect fit for the srew hole, and very little mess. I push in 60ml, then top up with another 40ml, useing CastolEP (ecstreme pressure) 80/90. If its too thick due to being too cold, bring it in near some heat for a while, that helps.
It only holds 100ml so to be safe, drain the lot, as described above and replenish with new oil, not forgetting to measure how much you are putting in!
I use a plastic syringe with a ml scale printed on the outside. You can get them from any good chemist. Don't go for a small one though as the oil is quite thick and would be difficult to 'suck-up'! I use a 50ml one, no probs!