I'm planning on flushing my tranny fluid in my 6 speed. I want to use GM syncromesh. Do I need to get any LSD additives for it?

 

Should I use the Honda reformulated fluid instead of GM sm?

 

Nope just the Gm stuff or the Acura stuff. I've heard the GM is better but I don't know. I used the Acura fluid when mine was changed.

 

I ran GM Synchromesh FM in my GS-R after the newer Honda/Acura MTF and it seemed maybe a little smoother.
I am now running this:https://www.amsoil.com/storefront/mtf.aspx. in my CL-S6. The Amsoil MTF seems to be noticeably smoother than when the Honda MTF was in it. Still the 6spd is pretty smooth no matter which you use.

 

GM Synchromesh is great... have had in my the CLS-6 for 2 years. It completely fixed the "notchiness" into second in cold weather.

 

honda reformulated mtf is good but still gm syncromesh>honda mtf