So back in the beginning of January, I changed my manual trans fluid and, after much back and forth, decided to go with Royal Purple Synchromax over Red Line MTL.
This was a tough decision as a lot of people have good things to say about Red Line, and Mike Miller recommends it and uses it in his cars.
What really pushed me towards the RP was that after reading a lot of posts on multiple car forums from people who switched from RL to RP, the consensus was that the trans shifted smoother and was much less notchy with RP. Well, that and the fact that Dane went with it.
My only concern was that there were a few threads where people felt that the RP broke down quickly around 10-15k miles. This was based on a return of notchy shifting and in one case some brass shavings observed in the fluid during a change (although the person did admit to grinding gears occasionally). There is no empirical evidence that I know of that documents this alleged break down.
So here's where I am, and where I'm going:
I've had the RP in for 4k miles now and am happy to report that it has, so far, been a great fluid with noticeable improvement over the oem fluid (which had almost 50k on it).
Shifting is noticeably smoother with no notchiness or difficulty getting into first. This includes during very cold weather.
My concern, obviously, is what condition the fluid will be in as I get in the 10-15k miles range.
In order to address that, my plan is to change out fluid at its half-life of around 15k miles and send it off to Blackstone for analysis. While that won't really tell us whether the RP is any better or worse than other fluids (we have no oem or RL results from 15k for comparison), it should be able to tell us whether the RP is breaking down prematurely.
I also know that Dane is running the same fluid and has the same concerns-- and may go the Blackstone route himself (which might give us an answer sooner as he piles on the miles much faster than I do).
So far, I would highly recommend the RP Synchromax.
We'll see how the lab results turn out down the road.