It ain't rocket science,, the "special" lubes are for "Positraction" type units, (also called "limited slip," ya know, the ones that use clutch plates that are clamped together where the shafts ride-up a ramp to apply pressure to the plates, those type diffs are not a locker, they just offer some torque bias between axle shafts, and the plates "slip" depending upon the pre-set springs which control the torque bias.
The G80, as used in the trucks is a real locker, except it uses flyweights, to control its action, so that its lock-up cannot occur at speeds greater than ~20mph or so.
It is called a "Gov-Lock", (it ain't a Posi,) and its made by Eaton, and they have been supplying GM with them as OEM equipment for many years, and it uses regular gear oil.
If you have to, pull the diff cover,, no clutch plates, no special lube.
The G80, as used in the trucks is a real locker, except it uses flyweights, to control its action, so that its lock-up cannot occur at speeds greater than ~20mph or so.
It is called a "Gov-Lock", (it ain't a Posi,) and its made by Eaton, and they have been supplying GM with them as OEM equipment for many years, and it uses regular gear oil.
If you have to, pull the diff cover,, no clutch plates, no special lube.