Bell and Colvill talked to MMC about the cracks in my tank brackets and MMC have offered to do a warranty repair even though the car is 2015. I just need to get up to Malvern. That seems pretty fair to me so thanks to MMC and B&C.
The repair seems to be “an aluminium sheet bonded to the bottom of the tank to support the cracked bracket”. I’ve thought about this and I think that this implies the problem as they see it is weight on the front bracket (probably when the tank is full). Those Of you that have stripped out the tanks did you notice that the front bracket was taking weight?