[Richbot]

I've taken apart several viscous diffs and the M diff doesn't operate anything like a viscous diff. There is no variable-viscosity fluid which physically provides the lockup on the M diff, the shear pump that is driven by wheel speed differential provides pressure to generate a clamping force to the clutch plates, and the clutch plates provide the lockup. The fact that the shear pump generates pressure based on wheel speed differential does not make it a viscous coupling since the shear fluid by itself has no effect on how the wheels are locked together. On a VLSD the fluid heats up with wheel speed differential, which changes its viscosity and makes it more difficult for the couple-dozen thin metal plates inside the diff to spin. The fluid itself provides the lockup. Completely different operating principle.

You can see why they'd blow up on the track eventually, especially without any additional cooling I bet that shear pump gets pretty hot and there's no way to relieve pressure since building pressure inside it is the whole point

There's a long history of not offering limited slips in fast mid-engine cars, the McLaren doesn't bother me, seems like a good solution to keep drivetrain weight and complexity down since most of the time (once up to speed anyway) the car will have enough traction on the inside wheel to keep it from turning over.