Axle Fluid
WARNING: This page does not describe the selected car, but rather 20 other vehicles, including the 1987 GMC Pickup, 1987 GMC Cab & Chassis, 1987 Chevrolet Pickup, 1987 Chevrolet Cab & Chassis, and 1986 GMC Pickup. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION:
Axle lubricant should be changed whenever the axle has been submerged in water. Water can enter through the axle vent hole and contaminate the lubricant.