I have a clanking sound in my rearend when turning. several years back I had this problem and I just drained and put in GM lube w/additive. this seemed to work ok but just wondering if there is some other product I should consider using. This is a 410 posi 12 bolt in a 69 z/28

 

GM is what I've used before, and even sometimes the generic additive that parts stores sell. The additive prevents the oil from gumming up the posi clutches, which makes them stick together. That's what gives you your clunk-clunk while turning.