actually, the recomended fluid is 75W-90 NOT 80W-90... there is a factory service bulletin that says to switch to the 75W grade if the customer complains of hard shifting in cold weather. also, there is a Redline Gear oil for hypoid gears, ie: differentials, and a Redline MTF, different grades of both. There is a specific Redline MTF that is geared for Mazda Transmissions. another thign to consider is the use of GL4 gear oil. From some reading I did, it seems like the GL4 stuff seems to work smoother than the GL5 stuff because the GL5 fluid is too slippery to properly engage the synchronizer blocking rings...(the brass/copper looking things that are part of the synchronizer assembly in your transmission)
Here's a pic:
MT-90 75W90 GL-4 Gear Oil is what you want to use for the trans, not recomended for hypoid gears.
75W90 GL-5 Gear Oil is what you want to use for the diff.
Personally, I could not afford Redline right now, so I used GL4 compatible Coastal Gear oil, 75W-90 grade, this stuff is good for a daily, and cheap if you want to flush out your drivetrain before putting in expensive stuff.
http://www.redlineoil.com/Products.aspx?pcid=7
There, bam... I feel like a fuckin expert on redline oils now, they should pay me for this!
