I think/hope that we are having some recycling of established problems:
I am unaware of any problems with the latter phase (2014+?) chassis that had welded in brace and I understand different gauge/quality tubing.
The original chassis was prone to cracking by the upper wishbone - many chassis have been replaced because of this
Other cars with the original chassis were fitted with a bolt-in brace. Some of these have exhibited cracking in 2 locations - firstly by the upper wishbone probably because cracking had been initiated before the brace was fitted (these required a new chassis) - secondly some have exhibited cracks on a vertical tube below the wishbone - this can be fixed by welding and I think Phil Bleazey has a good piece on how this can be done. I understand this second are of cracking has not been seen on the recent chassis because of the brace and/or tube gauge change and/or reinforcement.
The buyers guide on the MTWC site is good on this topic and given the history of this topic, regular inspections are a good idea....
