Searched the forum, got lots of great info as always. I have a 2006 NA Solstice with LSD and 5 speed. Previous owner had diff serviced in April 2013 at local dealer because it "started making a howling noise out of the blue." Dealer reported no metal or material in the oil, installed 75/140 "gear guard" and "limited slip concentrate" and sent him packing. My symptoms are whining at most any speeds and chattering / maybe even tire scrubbing at low speeds on hard turns. I was a GM Tech in the 90's and this is definitely LSD related. Lots of the posts I read were 5+ years old. Can anyone tell me the latest and greatest? Info on this? I know lube and additive are crucial. I was debating using Royal Purple 85W 140 if factory lubes don't work. Also, is there a good source for replacement units remanned or used if the damage is already done? I saw a post somewhere that said 2008 and up were redesigned and the unit is shared with a Cadillac platform? Thanks for the help.