I dont have all the answers.
I used Redline 75w90, seems to work fine.
Pulls great in the corners.
good suspension helps
325is 3.73 LSD original
Had a little chatter at first, 1-2 days (rain), now its smooth.
Redline web site says the 90 is "preffered for most racing applications" so I went with it. It doesnt say that for the 140? Not sure what it all means.
I was just told to be sure as hell it was "hypoid" for LSD applications and GL-5 or better. (thanks to my race buddy and BMWJNKY)
The race shop also had some "special stuff" in the back for the Fri night drag racers which I guess is stickier and helps lock em up, but bad for autoX
Seems the trick is to get it to stick just up to the point of getting chatter.
Redline site had an addative to make it slippier they say to add just enough to eliminate chatter without getting to slippery. I didnt try it, the straight 75W90 seems to be fine.
Oh but dam did the old stuff stink up the whole garage for days. LOL Red Line Oil
I used thier MTL in the tranny and all the cold syncro problems went away too, it was like freakin magic, thats when I decided to try thier diff lube.