I dont buy thermal shock cracking welds
My thoughts are that the top 6" of the radiator are completely unsupported- and MMC's fix to date has been to increasingly stiffen the mountings hence the welds cracking...
Also the Header tank is too small to accomodate for coolant expansion. I bet that during testing the cars kept spitting out coolant- hence they were delivered with a 25 odd lb radiator cap to try and keep the coolant in....
