My chassis crack was discovered in 2018 when it was spotted by RogG at the Goggles & Gauntlets rally in June that year.
The crack on mine was very similar to that of RogG's (as in his photo above). My mileage was then at around 15,000 and at that time I was aware of 4 other cars (i.e. 5 in total) with this same type and location of crack.
MMC insited that the cars should not be driven until they had repaired the crack and we had to get the cars to the factory at our expense.
The repair involved removing the existing wishbone mounting lugs and welding on a redesigned lug each side of the car, which had a much larger footprint with the chassis tubes.