although not to deeply I did search on this as I am sure its been touched on. But it seems all posts reflect a u joint or other drive shaft problem and I dont think that is it.
on decel or neutral (clutching) the LSD pops, of course going around turns also does it. I know that normal behavior for these things include noises and poping but to what extent? and would new fluid or switching to synth. quiet it down a little? How do I test it to see if its going out or already **** the bed?

by the way its an 81 GSL

 

do you have any LSD additive in the diff

the cluctches might be worn out

 

I dont have any additives and how do I check the clutches?

 

first get some LSD additive and add to your diff, i think redline makes some

 

I'm looking to purchase the car so I'm trying to determine if it needs a new rear or if its just a characteristic of the car that I can deal with.

 

The diff clutches do nothing in a straight line. Drive power does not go through the clutches, per se. The clutches only bind the side gears to the diff carrier, to try and prevent them from turning in relation to the carrier.

Your popping noise is probably due to hosed bushings or U-joints. Most likely bushings.