I wouldn't run that viscous LSD either...
The viscous LSD basically mimics and open diff at very low deltas.
http://fc3spro.com/TECH/MODS/DT/lsd.htm
The stock clutch-type LSD's are all basically worn out by now.
Most of them operate like an open diff due to the high mileage.
I believe the clutch discs are all "NLA" from Mazda?
-Ted