Is it good to buy a used transmission?
Remember that any used transmission is never as good as a new one. Nothing lasts forever and a part of its life is gone. You pose a considerable financial risk if you choose to buy the used transmission.
You may encounter significant risks of buying used transmission to resolve temporary issues. You will not know its actual history to predict its possible life expectancy. It may work only for a short timeframe, even as short as one year. Additionally, you cannot be sure if it even works for a single day. You could also easily make a mistake and buy the wrong transmission model which may not work with your car.