What transmission fluid are you all running?
 

Any recommendations for a dedicated track car?

I'm running OEM but next change I am going with Millers Nano CRX 75W90, but I have not yet so I can't give a first hand report on that. I put the OEM fill in 2014 and have maybe 50 track days on it, and plan to get a UOA when I change it. It hasn't given me any trouble with 20 minute sessions in summer, and sometimes I run 30+ in cooler weather if the car is staying cool.

These are my HPDE experiences and with stock.open diff.

I have a reward cert to redeem for Miller's Oils, so I plan to try that next as they have a good reputation. But in the meantime, I have been using Mobil Delvac 75W90, which came highly recommended and has served my SPB well so far.

This is interesting, as I have been going the other way.
I started out with Royal Purple Synchromax because I have had excellent results in other vehicles. It worked fine. After 2 years and 30 HPDE events, I drained and refilled with Porsche Fluid to see if there is any difference, knowing that it is the most recommended fluid for these transaxles.

oem in my 5 speed

I typically run OEM trans fluid.

I tried Millers Nano CRX 75W90 because (like trygve) I won a certificate from a race. In my experience, it worked fine - no better, no worse, than OEM.

(I had the same experience with Miller's motor oil - seemed to work just like any other high quality motor oil).

I used Motul the first time I changed - but went back to OEM when I had the trans rebuilt. It's hard to tell the difference - because of the rebuild but it's shifts great now.

OEM based on most discussions.

I've run Redline in all my race cars..

Currently using Redline 75w90NS. No complaints, but all I can compare it to was the unknown fluid that was in there prior for up to 97k Miles.

My last fill was with Millers nano75w90