When we had this problem on our '90, I first placed a large, clean piece of cardboard under
the transmission.  Then I could see exactly where the fluid was coming from which was
difficult because of all the grime.  After driving around alot, and parking overnight, the
puddle appeared.

For us, it turned out to be the o-ring from the governor cap.  On the upper, driver's side of
the transmission, there is a ~4" metal cap which goes over the governor.  The o-ring was
hard and brittle, and any fluid up in the cap just dribbled out.

HTH,

John Haddad