Trans and Diff Fluid Change...
 

In the on-going effort to accomplish most every task in the 101 Projects book (I don't think I'll be going forced-induction!!!) I am about to change the rear diff and tranny fluid in my 1998 328is. In the book and here on-line, Wayne recommends SWEPCO 201 multi-purpose gear lube, which sounds great; however, most forums I've read people are using mostly high-quality ATF fluids (Redline, Mobil 1, etc...) in their transmissions. So, my questions are:
1) Why should I use one or the other?
2) What will be the differences in shifting (I've heard that the heavier oils are harder to shift)?
3) Is the SWEPCO 201 similar to the 75w90 differential gear oils that people are using, or is it more (or less) viscous?

Any thoughts from people who have tried both would be great, and any general info is also appreciated!

DO NOT use Swepco in the tranny.

Read my comments here:
http://forums.pelicanparts.com/101-projects-discussion-forum-bmw-3-series/316094-shifting-gets-harder-after-manual-tranny-fluid-change-swepco.html

Best:
Redline
Amsoil

Nearly as good and plenty good for the average driver:
Royal Purple
Mobil 1
Most other name brands

You dont have limited slip but LS modifiers wont effect your diff so it doesnt matter. Let me know if you have any questions.

Thanks! I am installing the LSD in a couple of weeks. I've been happy running AMSOIL in my engine, so I think I will use it all around...

I'm assuming you have a manual tranny.

Try to pick a fluid that has syncro additives such as this:
Synthetic Manual Synchromesh Transmission Fluid (MTF)

It isn't what comes up with their online application guide but it appears to be something to consider. It is slightly thicker than ATF but it is designed for syncros.

Discuss it with your Amsoil rep.