Vehicle Speed Sensor
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1991 GMC Pickup, 1991 GMC Cab & Chassis, 1991 GMC C3500 HD, 1991 Chevrolet Pickup, and 1991 Chevrolet Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
Raise and support vehicle. At transmission tailshaft housing, unplug vehicle speed sensor harness. Remove hold-down bolt or unscrew vehicle speed sensor. Catch transmission fluid in suitable container. Remove "O" ring. To install, reverse removal procedure, and recheck fluid level.