Noise In Drive Train When Vehicle Downshifts

1992 S-10 Blazer 4x4, 4.3 with TBI and automatic trans. Vehicle has started making a clunking sound as I slow to come to a stop and the trans downshifts. At first I thought it was possibly a U-joint but when I inspected the driveshaft I found that there was a little more slack in the rearend. Thinking I had a problem with the ring gear and pinion,I pulled the cover. The carrier turned out to be a "Locker" type and the slack appeared to be in the side gear to axle spline.Ring and Pinion have good wear pattern and no broken teeth. I noticed that the side gear on the pass.side of vehicle has small clutches behind it and wondered if they might be my problem.Also wanted to know if this type of carrier has to have an additive with the gear oil like the early chevy   posi unit? Any info would be helpful.