Great explanation. Just to add that the reason slippers work as they do is the PTFE plates on either side. PTFE is a material that is able to move from sliding friction to static friction seamlessly. If it didn't, then the diff would lurch from slip to grip, and make teh cars almost undriveable.
I think the idea was pioneered by Losi, and I first saw one at the 1989 Worlds in Sydney, Australia. It was so obviously superior to anything else we did to make a car driveable on the slippery track. IIRC, Cecil Schumacher set about making one for Jamie Booth and Jamie tried it during qualifying. I can't remember whether Jamie used it to get his car into the A final, but I do remember that as one of the most heroic qualifying performances I have ever seen! HTH
