I guess I'll re-word the question a bit. Ignoring any specific viscosity requirements, are all "synchromesh" type fluids compatible with transmissions that specify a GL-4 fluid?
I think I explained this earlier:
they all have Performance Improvement or PI additive packages that give them a GL-4 protection rating, regardless of the viscosity, and regardless of whether or not they explicitly state such.
Stated another way, the answer is "YES," they have to be.
Here is what application-specific MTLs consist of:
1. Base oils of various types and viscosities to make a specific viscosity and have anti-shear properties
2. GL-4 Performance Improvement (PI additive package) chemistry which consists of the following
a) GL-4 anti-wear (AW) additives
b) anti-rust additive
c) copper and aluminum metal deactivator/buffering agent
e) special friction modifier (FM)
I don't know how much clearer I can make it.
BTW, Application Specific = Dedicated.