I imagine he meant finned
I'm not so sure how much love I'd be putting in that 40 year old video, I didn't know they were made by Eaton but all my chevy truck friends call them "gov lock" probably because the 100rpm differential between wheels is from a mechanical governor... Anywho, apparently they have a limited life span and just stop working after a while...
I reshimmed the limited slip in my '00 Explorer (and the one in the '91 Explorer I had) and it responds very nicely, Ford in all their wisdom stacked the shims steel on steel and friction on friction and left room for another disc on each side... when you stack them in a logical fashion as tight as you can they work much better... 40k miles after I put it together (with junkyard parts) it still puts power to both rear wheels and will whip the heavy pig sideways if you do it right...