Hello & Welcome to this Aerostar forum, Sailor Sailor,
I have a 93 & 95. My 93 is an AWD and recently ate it's transfercase. It has 260,000 US Miles, or 10,000 over a quarter million miles. I also have a 95 with 240,000 US miles on it. There are several Aerostars in the town I live in. Even some early ones 1985 -1991 are running around down here.
As for your Aerostar, transmission I'd suggest you not put any sort of Miracle Stuff from a can in your A/T to cure a problem. It may or may not make a difference in the short term, but it will not repair anything & long term it may do more harm than anything else. Mechanics & Technicians do not come in containers on a shelf.
I will state however, Big Problems very well can come in them. Adding "Seal Doctor" may in the short term cause seals to swell up slightly, but it reduces both longevity & functionality, plus it usually eventually destroys most friction surfaces on Bands & Clutches plus allows residue to contaminate valve bodies & servos which make an A/T work and actually function correctly.
Before I go any farther, what powertrain combination does your '92 Aerostar have in it ? What engine size & what drive train [RWD or AWD] ? When is it hesitant to engage only when Hot, or only when Cold, or Both @ Anytime?
CIAO
FBp