Nothing wrong with it. BMW uses them, and like you said, so do the later 300ZXtt. They work great, but have limitations. With a clutch type, you can shim the clutches to get more clamping force, thus decreasing the amount of slip. This is very cool if you want to adjust the amount of slip in your LSD. With a viscous type, you rely solely on the viscosity of the fluid, which may not be enough for very hard driving.
Problem with the Viscous vs Clutch type for us, is the viscous doesn't adapt into a early Z car, hence our preference for the clutch type. This is based on what I've heard, I've yet to find a LSD of any type in the junkyard.
Viscous diff is actually much better, you will get more lock up if you get dramatic wheel spin on one side . It does not wear out like a clutch pack, spring tension in the clutches are reduced over the years . The vicous uses a silicone based fluid to the heats up in small the causes a friction shearing of fluids . This friction locks the axles to the diff carrier.The reason why everyone says stay away from it is that your halfshafts won't properly lock into the diff . The inside snap ring is in the wrong place, I think it needs longer ends on the shafts . The vicous is better than clutch but custom shafts must be used . Just a little side not if you want full locking for drag racing you can get ARB air locker which completely locks the wheels together not recomended for slalom at all .
It's a matter of halfshafts fitting. By now we know that the 300z have alot longer halfshafts, right? Well with a clutch type LSD you can use 280 halfshafts with no problem. However the viscous rear uses oddball halfshafts. The splines that go into the rear are different than all the other R200 rears out there. The driver's side is almost twice as long as the passenger side (the actual stub that goes into the rear). if you try to insert standard stubs one side will only go in part way, and the other side will not go in anywhere near far enough. Of course you can take the viscous CV shafts and have them shortened, but it's a lot of work that's not necessary. If you have a 300z you can use the rear, but you have to swap CV shafts and companion flanges as well. As far as performance the viscous type is supposedly superior. The TT guys use it because that is what came in their cars. Us 240 guys use the clutch type because that is the only thing that will fit in our cars, bolt in that is...