The Suzuki Manual says:
Manual transmission and TC - 80W90, 75W85 or 75W90. It has to be GL4 - for the synchromesh to work, and last.
Diffs - GL5 90, 80W90 or 75W85.
There are some oils which are marked GL4 and GL5, but if it isn't marked GL4 it is NOT for the transmission and TC.
Similarly, if its not marked GL5, it is not suitable for the diffs, because of the shape of the teeth (can't remember the technical name)