I had a 'klunk' going on when starting up from stopped or when going into reverse, etc. Replaced the panhard rod bushings and I thought that took care of things, but no such luck... And driving along side some jersey barriers yesterday I could hear a rhythmic sound in time with wheel rotation, vaguely like a "creak," not too loud, didn't matter if the car was in gear or out. So I've got it up on stands to take a look and do some other stuff. On either side, when I turn the wheel/drum by hand there is considerable 'play' before I feel anyhting "engage" in the diff. and if I pull out or push in on the drum there is a tiny, tiny bit of play too. Seems to me there should be little play in the former situation and no play in the latter, but what is the likely culprit here that's worn?

Also, I was going to change the oil in the differential- Haynes calls for 90 wt Hypoid B, but I'll I'm finding at the local car parts places are multi-grades (85w90, 80w140, GL-this that and the other....). Is there an acceptable substitute?
Thanks
Tom
NYC