I posted about this problem a while back... a 2013 made Masport 4 blade mower that cracked the blade carrier around the washer ...I actually welded the piece back in, ground it off and made a larger washer for it... I have since found another one with exactly the same problem.
I have also seen an earlier 2 blade carrier that has done the same thing.. but to be fair , this particular one was not fitted with a flat washer .. The bolt was fitted with a spring washer and was so over tightened that it had a "wad punch effect" on the carrier, starting a crack around the damage.
Just another thing, all the Masports that I have had or seen over the years, all seem to crack the body on the left hand rear side, just forward of the wheel.
Ken