[cnavarro]

I'd use the M1 Delvac 75w90 (which superseded the SHC product). I'm currently running it in my C4 in both differentials and love it. I tried Redline and found it too notchy in the G50, but I've used it in other cars and have been very happy with its performance.

Lufteknic is the only place you can get the Delvac product in gal jugs. I get it from the big rig shop next door, as they have it in 55 gallon drums and they pump it right in to my 911 - cost me a whopping $23 last time they changed the fluid for me.