[LH Lead-Foot]

To seal the flange to the pinion, the service manual indicates GM #12346004. It is a liquid teflon sealant. They don't list copper paste.
While formulas of wheel bearing grease are different so as to not copy someones patent, it is still used without failure to bearings or friction materials used on GM corporate limited slips plates or Auburn cone type. I have no opinion, just hands on experience rebuilding rear axles that most pay less than 4hrs. book time to complete. 4.8hrs if limited slip with exciter ring for three channel ABS.

Question, If you have full floating axles, how does the bearings get lubricant? They are on the outside of the axle where gear lube does not flow. The only gear lube that comes out is when you un-bolt the axles. They will burn up with a few days of usage is you don't pack them.

It is just an issue of protection for the bearings before the centrifugal splash flow of GL5 start to sling into the nose of the differential housing to begin to lube the pinion bearings. No one uses 3 lbs. of grease on these bearings, just a coating for initial bearing alignment, seating and reducing rotation force. While gear lube maybe common, it's just fine. Use what you want, I don't care. I have never had any problem after decades. Mine works fine.

Perhaps you can explain the factory ring & pinion "Zero" backlash used on the 1972 Subaru GL Wagon and the Lancia Beta. Or the best way to remove the cylinder head off the 9" block studs on the Fiat X1/9th?