I don't like to throw a spanner in the works, especially with all the testing that you have done Hippo. However I'm a little concerned that you might be looking for a figure that simply isn't there to find. I'll try to explain how I perceive the VCU functions. The fluid is a special fluid that hardens as it is agitated. This is call a non-Newtonian fluid. This fluid hardens locally between alternating plates inside the VCU. Now from the research I've done over the last few years, the VCU doesn't lock or "activate" in the same way as a clutch for instance. It works more like an auto gearbox torque converter. Essentially the more torque that is applied the less it slips so the output torque increase. This only happens up until the torque / slip equilibrium is reached. So in effect, a correctly working VCU will always allow an amount of slip, even if it's taking plenty of torque. It has to have some slip for the fluid to be agitated. If there is little agitation, drive transfer can't take place. It's these very properties that make the VCU so good at what it does. I believe that the fluid only has a limited life as a non-Newtonian fluid before it's properties start to degrade. As fluid degradation takes place, the fluid starts to thicken, transferring more torque than it was designed to do. So basically it's slip/ torque equilibrium shrinks causing increased torque transfer. This is where the Freelander's design foibles come into play. As we know, LR in there wisdom geared the front and back slightly differently. This forces the rear half of the VCU to over run, or drive the front half. As the VCU ages, it's less likely to allow for this gearing mismatch, so starts overloading the gears in the IRD and rear diff. Eventually something it the drive train goes bang due to the sustained added stress.
There appears to be only 2 reasonably reliable tests for the VCU, ideally used together for improved accuracy. The OWUT and VCU temperature measurement. The OWUT loads the VCU while monitoring the slip rate, this is a valid test as far as I can tell. Meanwhile measuring the temperature is also going to give an indication of the VCUs ability to slip. If it stays cold, no or at least little slippage is occurring and the drive train is taking a pounding. The VCU can't actually seize solid or the wheels would skip and something would break very quickly. Wheel skipping does happen when turning on a tight lock with a failed VCU.
I hope I've not ruined all your hard work but this is how I perceive the VCU function and how we can check it at home.
I could be completely wrong of course.
