Ok I've managed to test the Tech Racing ring gear plate on the front diff.
The verdict? It works but does not completely solve the problem.
It does protect again minor frontal taps but does nothing for harder taps. This still makes it a worthwile investment.
This is because of what Difuser said. On high traction tracks the tires of the car bite into the surface and transfers and incredible load onto the front diff gears which is the weakest point of the car.
On low traction tracks the tires may break traction and wheelspin which may protect the front diff gear.
Using a full diff at the front helps because the diff can slip a little when you hit something. With a one way there is no slip.
The front diff is just not strong enough to handle the load. If Tamiya are working on a fix it will most likely involve replacing the front gear with one that is significantly stronger. This may end up transferring the load elsewhere along the chassis which could move the problem elsewhere
In any case I'm still happy with the Evo3...although I would be happier if I didn't have to replace the diff gear after every race meet
The results from the Thai race shows what it can do in more capable hands (ie. a person that crashes less).