such as Redline MT-90. Go to myoilshop.com and do some reading. That gear lube from Mobil is equivalent to 75W-90 differential fluid from Redline. Differential fluid has a special additive that is not compatible with manual transmissions. Although they are the same weight, the fluid is not compatible. 75W-90 is just a weight...nothing more! You have to buy the right fluid for the right application.
If you go to myoilshop.com, you will see the difference between MT-90 and 75W-90 differential fluid (or gear lube).