[bono83]

I'm not sure about Mobil 1, but I am sure about Redline because that's what I used for my M6 V6. I used the 75w90NS (Non Slip) in the manual trans and the 75w90 in the rear end. The NS has no friction modifier and should be used in the transmission. The regular 75w90 has friction modifier in it for the limited slip differential. If you use the NS in a limited slip differential rear end, you'll get "chatter" when turning. If you used friction modifier in the manual transmission, it won't shift right because it's too slippery and the syncronizers won't slow don't for proper engagement.

I changed mine at about 6200 miles. I was hoping for better shifting when it was real cold out, but I didn't notice much of a difference. The trans fluid was pretty clean and I don't think it's necessary to change it unless you're really driving your car hard. The rear end fluid and tons of metal shavings in it and I wished I had changed it at about 500 miles. Hope this helps.