For MT-90? NoDo these Mazdaspeed Protege transaxles with LSD's need a friction modifier if I'm using Redline MT-90?
It might have to do with the type of LSD system it is. The MSP's are gear driven and I believe there is a fluid driven design, which needs a modifier.
Use Any GL-5 Fluid.maybe it would be a good thing to post up known brand names that are ok to use
to straighten out some facts here:
Redline MT-90 is GL-4
Royal Purple MaxGear 75w-90 is GL-4/5
watch what gl-5 fluids you use because the high sulphur content will eat away at brass syncro's (not sure if ours are brass, still trying to confirm that) Royal Purple MaxGear is a gl-5 compliant that will not eat syncros
edit: adding friction modifier will not harm anything but it's not required.