If your modulator is working ok, but leaking transmission fluid, you may only need to replace the inexpensive oring ( o ring ). You do have to be careful when removing the modulator from the transmission. For instructions (available separately) see related products below. For testing modulator pressure Kent has developed a DIY testing kit (see below).
For re-sealing green and black modulators on most 1981 to 1993 models.
123 107 126 201 124 722.3x and 722.4x Transmission Modulator O-ring Seal