1980's 7

I've searched through a billion threads but I need to know how tell if an LSD is dead. There is an 88 coupe here in a local junkyard that has an LSD rear end. I usually spin the wheels on each car I look at the see if they have LSD with out crawling under the car and both wheels spin forward on this car so it's still grabbing somewhat, but I want to know if there is any way to tell the extent of the wear before I pull it off.

I'll probably buy it anyway cause it's cheap and a slipping or fried LSD is no different than the open diff(spare parts never hurt anyone) I have now so I don't really lose. I just wanted to learn some information on the subject.