My only diff failure in multiple decades of abusing them was the failure of the crush sleeve on my 85's rear diff. This little 4 banger munched a r&p ( my first ) in this truck. I've not lunched a diff as bad with Huge cube V8s, it was a mess. 
Solid pinion spacers rule. 
I understand the crush sleeve paranoia.... BUT there are millions and millions of differentials with crush sleeves that don't have catastrophic failure and go 100s of thousands of miles with zero failures. ....... Can you explain why?
Like many topics, this one has been discussed and masterbated over and over....
Example:
http://www.hotrodders.com/forum/crush-sleeve-vs-shimmed-spacer-181485.htmlGnarls.
