Hi,

A transmission fluid change is the life blood of any transmission.
If the unit has any suspicion of being abused, by any prolonged intervals, it is your only choice to have it completely redone to get good lubricant in there. The filter screen not only should be changed but looked at for signs of clutch lining being caught.

It is my understanding that the Aisin transmissions are possibly made by Toyota. The repair kits themselves are relatively inexpensive, if one is needed, to restore them into like new performance.

The fluid change/inspection along with a linkage check/adjustment would be money well spent.
Doing the fluid change yourself is a parts cost only option.
Getting a real good manual and having a proper work space to go deeper, needs to be weighed against what is found during the service.

It's also my understanding that there are as many of these transmissions around like fleas on a dog.
Looks for prices driven by competition among the many garage kennels!
(:-)

Phil