I had a 1971 olds cutlass that over flowed thru the tube where you put fluid at (don't know if this is the same) but a transmission has to breath. If that tube gets clogged it will throw the fluid out, either thru the filler tube or front or rear transmission seal. My olds t/mission had a little tube about the size of a pencil on the left top of t/mission and it had a check valve in it and it got stuck closed.
I got some (for the life of me I can not think of the name oil) but it comes in a spray can and it loosens whatever is stuck and spayed it in that tub and walla, that did the trick. (It's a penetrating oil)
Transmission fluid, if you have a bad radiator.
Ford windstar
It is important to keep fluids from leaking from a car. Excessive transmission fluid would be coming out of the overflow because there is too much fluid in the transmission, or because the seal has become worn.
If you over fill your transmission fluid, you might blow out the transmission seals. It is most likely that some fluid will overflow, but no damage will occur.
Transmission fluid is low, dirty filter, leaking seals, sticking accumulator, etc.
The Windstar transmission could have a seal that leaks worse as the transmission gets hot and the fluid is under pressure. Go to a car wash and clean the transmission good. Watch for several days to see where the fluid is leaking from so that you can find and fix the leak.
According to the 2001 Ford Windstar Owner Guide : ( Motorcraft MERCON-V is used in the automatic transaxle / transmission )
Motorcraft MERCON automatic transmission fluid in the 1999 Ford Windstar power steering ( according to the Owner Guide )
Check or change transmission fluid and filter
broken radiator
Replace radiator ASAP. And flush tranny fluid.
NO. You must drain it out to the correct level. To much fluid will damage the transmission before it pushes the fluid out of the vent tube.