I have always used Mobil1 diff fluid on the S. The Amsoil is GREAT, but it is EXTREMELY viscous and is not reccomended if you drive you car when it's cold out. I am not clear on the definition of "cold" used for that criteria. However, I did help a local S2000 owner put the stuff in his car, and it was considerable thicker than the Mobil1. I would be uncomfortable personally running it below ~ 45 deg or so.

I have always used the Honda MTF, but at my next change I plan to switch to the GM Syncromesh Friction Modified.

The Diff takes a LOT of abuse just driving the car. I changed mine at about 3500mi the first time and it was NASTY black. I now change it every year (which for me is about every 4,000mi) and while filthy, the fluid is never as bad as that first one was. I change the transmission and engine oil at the same time, just before storage every year.

BTW -- For engine oil, I like Castrol GTX for cars with less then ~ 10,000 mi on them. When they still burn oil. Once the car stops burnin oil (typically around the 10,000mi mark) I switch to Mobil1. Since I rolled JUST over 10K on my car last year, I am now running Mobil1 in the car. Switching to Mobil1 "early" (while the car is still burining oil) will cause it to burn MORE oil, and will cause it to burn the oil for a longer timeframe than the rough estimate of 10k mi.

 

I just put Redline MTL in my car yesterday and I am liking it better than the Honda MTF I put in last year. Like every other fluid, some people like it and some people don't. Since you like thei products give it a try and go from there.

 

so many choices...i think i'm going to go ahead with the gmsmfm in the trans, either mobil 1 or supertech in the diff, and mobil 1 in the motor with an oem honda oil filter. dang i have a lot of shopping to do.

 

All in all, it looks like you're getting a lot of suggestions one way or another. I suggest either sticking with what you have if you're happy with the trans and diff operation as it stands.

Otherwise, try different ones over a shorter period of time (let's say every 3000 miles). This way you'll be able to try all the "regular" stuff and move up step by step until you find something you like until get to using a high-end product like AMSOIL if you so choose.

One more tid-bit I want to add for the GM Synchromesh suggestion. Suja 1 suggests not using GM Synchromesh until you develop a grinding or a "notch" problem in your gears. GM Synchromesh (with friction modifiers) helps alleviate any issues once you do, however, they suggest sticking with OEM if nothing is wrong.

Also, Sunday afternoon is great. I'll get the BBQ going if there's no rain. Others are welcome to join.