When I purchase a used car I like to change out all fluids brake, diffrential, powersteering,antifreeze, oil, tranny. that way you have a baseline and know your car fluids are new. No tranny problems to my knowedge I have 1993 gs with 175000 mi and also 1998 sc300 with 80,000mi. both run great knock on wood.
Just drain and fill (about 2 quarts) use toyota type 4 atf.