The grey parts supplied with the D spec are actually advertised as reinforced parts if you check tamiya.com! It was thought that they reinforced this piece due to similar experiences to what you've described Johny.

I've been rally bashing two TT02’s for a while now, set up as Blue describes without any problems (hopefully I haven't just jinxed myself!).
However note I also run mine with a TT01 'square' branded suspension guard specifically to reduce the impact to this sensitive area.
They're available at banzai hobby.

Good luck!
Crouch