Most of us prefer Redline Synthetic Oil products for use in the manual transaxle because it improves shiftability and gives you a plus of a synthetic oil in the manual tranny. BUT Mobil does NOT recommend it in a transmission that requires GL-4. Go here for more info. The SR20DE's tranny requires approximently 4 quarts of oil. I have spent a week now with MT90 in my trany.
Shifts are much more smooth and there is no mollassis shifting start-ups anymore.
It provides low temperature shiftability equal to an ATF, yet will not thin out or shear at high temperatures and provides the substantial gear protection of a GL-4 gear oil. The higher synchronizer coefficient of friction allows faster upshifting and downshifting and the lubricant is non-corrosive to synchros and bushings. Uses the same chemistry as MTL , but is a 90 WT in order to satisfy certain manufacturers which recommend SAE 90 GL-4 gear oils. The relatively constant viscosity over a wide temperature range allows easier shifting and helps prevent whine and rattle at high temperatures. Most gear oils, ATFs, and motor oils are too slippery for proper synchro engagement - which causes gear clash when shifting.