I'm wrapping up a ground up resto on a 69 SS. Converted from an Auto to a TKO500 and will ready to crank it up later today. Rushed off to the Chevy dealer and asked for the Synchromesh tranny fluid. Got home and found out the fluid I bought is the Friction Modified version part #12377916. Being that Part #12345349 is the version called for my question is this... Try the 12377916, or use the penzoil or 12345349 syncro fluid in the Camaro , and try the 12377916 in my `07 5speed mustang and probably enjoy much better shifting over the mercon in it now. Or maybe somebody out there has tried the friction modified version and can advise. Thanks...Awsome site I might add.

I believe the 12377916 is for the German Getrag tranny. Tremec recommends the 12345349 or if you wish the Penzoil synchromesh. I wouldn't use the 12377916.
Jim

Seems we all venture off and try to use some other Sycro fluid for the TKO for what ever reasons. But most of the time, you will come back to use the GM fluid.