[wiswind]

The Windstar manual calls for the fluid to be changed AT LEAST every 30K miles for normal service....and every 21K miles for "severe" service.
In the case of this unit....with 100K miles on it......these transmissions often fail at this point.
Mine did.....even with the 30K mile service done (60K and 90K also).

In your case.....I would change it several times.......1-2K miles apart.
This is because......there may be some sludge built up.
The issue with problem right after a fluid change at high miles......often people don't change the fluid until the transmission shows signs of problems........
Also.....the new fluid has a fresh additive package......and will clean the junk that the old worn out fluid left........which can cause the new fluid to become loaded up with junk.........
So....a couple of fluid changes will flush this junk out.
I use a in-line filter that is made by Magnefine......installs in the cooler line.
This will help filter junk out of the fluid.....but again......with this many miles....that little filter will need changing in SHORT order.......500 miles to 1K miles.
I have step by step instructions with pictures that show the transmission fluid exchange process......in the pictures that the link in my signature takes you to.

I have added a dose of Auto-RX to my fluid at 1000-1500 miles before a fluid change......which will do wonders to clean the buildup around the solenoids.