This time last year I bought a SG unit from Cass (Dr. Diff). I was told that it was the last one he had on the shelf and that he wouldn't be getting any more for at least six months. Supply chain issues etc.
Mopar 8 3/4" (8.75) Clutch Type Sure-Grip ("Powr-lok")
We ended up sending it back to him because the ring gear dropped right on. Despite being told that the bolts would hold it in place, my rear end guy didn't feel comfortable assembling the unit. Cass sent me a return shipping label and offered me a refund. I put the money towards one of his helical sure grip units.
Mopar 8 3/4" (8.75) Helical Gear Sure-Grip ("Sure-Trac")
I don't believe you're going to get that kind of customer service from an eBay seller.